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The amino acid betaine derived from glycine." []

Guanosine (G), also known as 2-amino-inosine, belongs to the class of organic compounds known as purine nucleosides. Purine nucleosides are compounds comprising a purine base attached to a ribosyl or deoxyribosyl sugar moiety. Guanosine consists of a guanine base attached to a ribose (ribofuranose) ring via a beta-N9-glycosidic bond. Guanosine is a white, crystalline powder with no odor and mild saline taste. It is very soluble in acetic acid, and slightly soluble in water, but insoluble in ethanol, diethyl ether, benzene, and chloroform. Guanosine exists in all living species, ranging from bacteria to plants to humans. High levels of guanosine can be found in clovers, coffee plants, and the pollen of pines. It has been detected, but not quantified in, several different foods, such as leeks, garlic, chicory roots, green bell peppers, and black-eyed peas. Guanosine plays an important role in various biochemical processes including the synthesis of nucleic acids such as RNA and intracellular signal transduction (cGMP). The antiviral drug acyclovir, often used in herpes treatment, and the anti-HIV drug abacavir, are both structurally similar to guanosine. Guanosine can be phosphorylated to become guanosine monophosphate (GMP), cyclic guanosine monophosphate (cGMP), guanosine diphosphate (GDP), and guanosine triphosphate (GTP). In humans, guanosine is involved in intracellular signalling through the adenosine receptors A1R and A2AR (PMID: 31847113). Evidence from rodent and cell models has shown a number of important neurotrophic and neuroprotective effects of guanosine. In particular, it is effective in preventing deleterious consequences of seizures, spinal cord injury, pain, mood disorders and aging-related diseases, such as ischemia, Parkinson’s and Alzheimer’s diseases (PMID: 27699087). Studies with rodent models of Parkinson’s disease have shown that guanosine decreases neuronal apoptotic cell death and increases dopaminergic neurons at substantia nigra pars compacta, accompanied by an improvement of motor symptoms in Parkinson’s disease (i.e. a reduction of bradykinesia). Guanosine promotes neurite arborization, outgrowth, proliferation and differentiation. Systemic administration of guanosine for eight weeks (8 mg/kg) has been shown to stimulate neuroprogenitors proliferation in the subventricular zone (SVZ) in a mouse model of Parkinsonism (PMID: 27699087). The effect of guanosine treatment is accompanied by an increased number of fibroblast growth factor (FGF-2)-positive cells which is an important regulator of neuroprogenitor/stem cell proliferation, survival and differentiation (PMID: 27699087). Guanosine prevents reactive oxygen species (ROS) generation and cell death in hippocampal slices subjected to the oxygen/glucose deprivation (PMID: 31847113).

Racemethionine, also known as DL-methionine or hmet, belongs to the class of organic compounds known as methionine and derivatives. Methionine and derivatives are compounds containing methionine or a derivative thereof resulting from reaction of methionine at the amino group or the carboxy group, or from the replacement of any hydrogen of glycine by a heteroatom. Methionine is an alpha-amino acid with the chemical formula HO2CCH(NH2)CH2CH2SCH3. This essential amino acid is classified as nonpolar. Racemethionine exists in all living organisms, ranging from bacteria to humans. Racemethionine is a mild, acidic, and sulfurous tasting compound. Racemethionine is found, on average, in the highest concentration within a few different foods, such as wheats, oats, and ryes and in a lower concentration in spinachs, white cabbages, and green zucchinis. Racemethionine is used as a flavouring ingredient and dietary supplement.

Nicotinic acid, also known as niacin or vitamin B3, is a water-soluble vitamin whose derivatives such as NADH, NAD, NAD+, and NADP play essential roles in energy metabolism in the living cell and DNA repair. The designation vitamin B3 also includes the amide form, nicotinamide or niacinamide. Severe lack of niacin causes the deficiency disease pellagra, whereas a mild deficiency slows down the metabolism decreasing cold tolerance. The recommended daily allowance of niacin is 2-12 mg a day for children, 14 mg a day for women, 16 mg a day for men, and 18 mg a day for pregnant or breast-feeding women. It is found in various animal and plant tissues and has pellagra-curative, vasodilating, and antilipemic properties. The liver can synthesize niacin from the essential amino acid tryptophan, but the synthesis is extremely slow and requires vitamin B6; 60 mg of tryptophan are required to make one milligram of niacin. Bacteria in the gut may also perform the conversion but are inefficient.

An amino-acid betaine that is butanoate substituted with a hydroxy group at position C-3 and a trimethylammonium group at C-4." []

Methionine (Met), also known as L-methionine, is an alpha-amino acid. These are amino acids in which the amino group is attached to the carbon atom immediately adjacent to the carboxylate group (alpha carbon). Amino acids are organic compounds that contain amino (–NH2) and carboxyl (–COOH) functional groups, along with a side chain (R group) specific to each amino acid. Methionine is one of 20 proteinogenic amino acids, i.e., the amino acids used in the biosynthesis of proteins. Methionine is found in all organisms ranging from bacteria to plants to animals. It is classified as an aliphatic, non-polar amino acid. Methionine is an essential amino acid (there are 9 essential amino acids), meaning the body cannot synthesize it, and it must be obtained from the diet. It is required for normal growth and development of humans, other mammals, and avian species. In addition to being a substrate for protein synthesis, methionine is an intermediate in transmethylation reactions, serving as the major methyl group donor in vivo, including the methyl groups for DNA and RNA intermediates. Methionine is a methyl acceptor for 5-methyltetrahydrofolate-homocysteine methyltransferase (methionine synthase), the only reaction that allows for the recycling of this form of folate, and is also a methyl acceptor for the catabolism of betaine. Methionine is the metabolic precursor for cysteine. Only the sulfur atom from methionine is transferred to cysteine; the carbon skeleton of cysteine is donated by serine (PMID: 16702340 ). There is a general consensus concerning normal sulfur amino acid (SAA) requirements. WHO recommendations amount to 13 mg/kg per 24 h in healthy adults. This amount is roughly doubled in artificial nutrition regimens. In disease or after trauma, requirements may be altered for methionine, cysteine, and taurine. Although in specific cases of congenital enzyme deficiency, prematurity, or diminished liver function, hypermethioninemia or hyperhomocysteinemia may occur, SAA supplementation can be considered safe in amounts exceeding 2-3 times the minimum recommended daily intake. Apart from some very specific indications (e.g. acetaminophen poisoning) the usefulness of SAA supplementation is not yet established (PMID: 16702341 ). Methionine is known to exacerbate psychopathological symptoms in schizophrenic patients, but there is no evidence of similar effects in healthy subjects. The role of methionine as a precursor of homocysteine is the most notable cause for concern. Acute doses of methionine can lead to acute increases in plasma homocysteine, which can be used as an index of the susceptibility to cardiovascular disease. Sufficiently high doses of methionine can actually result in death. Longer-term studies in adults have indicated no adverse consequences of moderate fluctuations in dietary methionine intake, but intakes higher than 5 times the normal amount resulted in elevated homocysteine levels. These effects of methionine on homocysteine and vascular function are moderated by supplements of vitamins B-6, B-12, C, and folic acid (PMID: 16702346 ). When present in sufficiently high levels, methionine can act as an atherogen and a metabotoxin. An atherogen is a compound that when present at chronically high levels causes atherosclerosis and cardiovascular disease. A metabotoxin is an endogenously produced metabolite that causes adverse health effects at chronically high levels. Chronically high levels of methionine are associated with at least ten inborn errors of metabolism, including cystathionine beta-synthase deficiency, glycine N-methyltransferase deficiency, homocystinuria, tyrosinemia, galactosemia, homocystinuria-megaloblastic anemia due to defects in cobalamin metabolism, methionine adenosyltransferase deficiency, methylenetetrahydrofolate reductase deficiency, and S-adenosylhomocysteine (SAH) hydrolase deficiency. Chronically elevated levels of methionine in infants can lead to intellectual disability and other neurological problems, delays in motor skills, sluggishness, muscle weakness, and liver problems. Many individuals with these metabolic disorders tend to develop cardiovascular disease later in life. Studies on feeding rodents high levels of methionine have shown that methionine promotes atherosclerotic plaques independently of homocysteine levels (PMID: 26647293 ). A similar study in Finnish men showed the same effect (PMID: 16487911 ).

Uracil, also known as U, belongs to the class of organic compounds known as pyrimidones. Pyrimidones are compounds that contain a pyrimidine ring, which bears a ketone. Pyrimidine is a 6-membered ring consisting of four carbon atoms and two nitrogen centers at the 1- and 3- ring positions. Uracil is a common naturally occurring pyrimidine found in RNA. It base pairs with adenine and is replaced by thymine in DNA. Uracil is one of the four nucleobases in RNA that are represented by the letters A, G, C and U. Methylation of uracil produces thymine. The name "uracil" was coined in 1885 by the German chemist Robert Behrend, who was attempting to synthesize derivatives of uric acid. Originally discovered in 1900, uracil was isolated by hydrolysis of yeast nuclein that was found in bovine thymus and spleen, herring sperm, and wheat germ. Uracil exists in all living species, ranging from bacteria to plants to humans. Uracil's use in the body is to help carry out the synthesis of many enzymes necessary for cell function through bonding with riboses and phosphates. Uracil serves as an allosteric regulator and a coenzyme for many important biochemical reactions. Uracil (via the nucleoside uridine) can be phosphorylated by various kinases to produce UMP, UDP and UTP. UDP and UTP regulate carbamoyl phosphate synthetase II (CPSase II) activity in animals. Uracil is also involved in the biosynthesis of polysaccharides and in the transport of sugars containing aldehydes. Within humans, uracil participates in a number of enzymatic reactions. In particular, uracil and ribose 1-phosphate can be biosynthesized from uridine; which is mediated by the enzyme uridine phosphorylase 2. In addition, uracil can be converted into dihydrouracil through the action of the enzyme dihydropyrimidine dehydrogenase [NADP(+)]. Uracil is rarely found in DNA, and this may have been an evolutionary change to increase genetic stability. This is because cytosine can deaminate spontaneously to produce uracil through hydrolytic deamination. Therefore, if there were an organism that used uracil in its DNA, the deamination of cytosine (which undergoes base pairing with guanine) would lead to formation of uracil (which would base pair with adenine) during DNA synthesis. Uracil can be used for drug delivery and as a pharmaceutical. When elemental fluorine reacts with uracil, it produces 5-fluorouracil. 5-Fluorouracil is an anticancer drug (antimetabolite) that mimics uracil during the nucleic acid (i.e. RNA) synthesis and transcription process. Because 5-fluorouracil is similar in shape to, but does not undergo the same chemistry as, uracil, the drug inhibits RNA replication enzymes, thereby blocking RNA synthesis and stopping the growth of cancerous cells.

Isonicotinic acid is a metabolite of isoniazid. Isonicotinic acid is an organic compound with a carboxyl group on a pyridine ring. It is an isomer of nicotinic acid. The carboxyl group for isonicotinic acid is on the 4-position instead of the 3-position for nicotinic acid (Wikipedia).

Approximately 95% of nitrobenzene is consumed in the production of aniline, which is a precursor to rubber chemicals, pesticides, dyes, explosives, and pharmaceuticals. Nitrobenzene is an organic compound with the chemical formula C6H5NO2. It is a water-insoluble pale yellow oil with an almond-like odor. It freezes to give greenish-yellow crystals. It is produced on a large scale from benzene as a precursor to aniline. In the laboratory, it is occasionally used as a solvent, especially for electrophilic reagents. Nitrobenzene is prepared by nitration of benzene with a mixture of concentrated sulfuric acid, water, and nitric acid. This mixture is sometimes called 'mixed acid.' The production of nitrobenzene is one of the most dangerous processes conducted in the chemical industry because of the exothermicity of the reaction ( delta H = 117 kJ/mol).

5-Aminopentanoic acid (or 5-aminovalerate) is a lysine degradation product. It can be produced both endogenously or through bacterial catabolism of lysine. 5-aminovalerate is formed via the following multi-step reaction: L-lysine leads to cadverine leads to L-piperideine leads 5-aminovalerate (PMID:405455). In other words it is a metabolite of cadaverine which is formed via the intermediate, 1-piperideine (PMID:6436440). Cadaverine is a foul-smelling diamine compound produced by protein hydrolysis during putrefaction of animal tissue. High levels of 5-aminovalerate in biofluids may indicate bacterial overgrowth or endogenous tissue necrosis. In most cases endogenous 5-aminovalerate is thought to be primarily a microbial metabolite produced by the gut or oral microflora, although it can be produced endogenously. 5-aminovalerate is a normal metabolite present in human saliva, with a tendency to elevated concentration in patients with chronic periodontitis. Bacterial contamination and decomposition of salivary proteins is primarily responsible for elevated salivary levels (PMID 3481959). Beyond being a general waste product, 5-aminovalerate is also believed to act as a methylene homologue of gamma-aminobutyric acid (GABA) and functions as a weak GABA agonist (PMID:4031870). It is also known as an antifibrinolytic amino acid analog and so it functions as a weak inhibitor of the blood clotting pathway (PMID:6703712). 5- aminovalerate is an in vivo substrate of 4-aminobutyrate:2-oxoglutarate aminotransferase (PMID:4031870). It can be found in Corynebacterium (PMID:27717386).

9-beta-D-arabinofuranosylguanine is a purine nucleoside in which guanine is attached to arabinofuranose via a beta-N(9)-glycosidic bond. It inhibits DNA synthesis and causes cell death. It has a role as an antineoplastic agent and a DNA synthesis inhibitor. It is a beta-D-arabinoside and a purine nucleoside.

An optically active form of methionine having D-configuration." []

Crotonoside is a purine nucleoside. Crotonoside is a natural product found in Croton tiglium with data available.

4-amino-pentanoic acid

Aspartic acid (Asp), also known as L-aspartic acid or as aspartate, the name of its anion, is an alpha-amino acid. These are amino acids in which the amino group is attached to the carbon atom immediately adjacent to the carboxylate group (alpha carbon). Amino acids are organic compounds that contain amino (–NH2) and carboxyl (–COOH) functional groups, along with a side chain (R group) specific to each amino acid. L-aspartic acid is one of 20 proteinogenic amino acids, i.e., the amino acids used in the biosynthesis of proteins. Aspartic acid is found in all organisms ranging from bacteria to plants to animals. It is classified as an acidic, charged (at physiological pH), aliphatic amino acid. In humans, aspartic acid is a nonessential amino acid derived from glutamic acid by enzymes using vitamin B6. However, in the human body, aspartate is most frequently synthesized through the transamination of oxaloacetate. A non-essential amino acid is an amino acid that can be synthesized from central metabolic pathway intermediates in humans and is not required in the diet. As its name indicates, aspartic acid is the carboxylic acid analog of asparagine. The D-isomer of aspartic acid (D-aspartic acid) is one of two D-amino acids commonly found in mammals. Aspartic acid was first discovered in 1827 by Auguste-Arthur Plisson and Étienne Ossian Henry by hydrolysis of asparagine, which had been isolated from asparagus juice in 1806. Aspartate has many biochemical roles. It is a neurotransmitter, a metabolite in the urea cycle and it participates in gluconeogenesis. It carries reducing equivalents in the malate-aspartate shuttle, which utilizes the ready interconversion of aspartate and oxaloacetate, which is the oxidized (dehydrogenated) derivative of malic acid. Aspartate donates one nitrogen atom in the biosynthesis of inosine, the precursor to the purine bases which are key to DNA biosynthesis. In addition, aspartic acid acts as a hydrogen acceptor in a chain of ATP synthase. Aspartic acid is a major excitatory neurotransmitter, which is sometimes found to be increased in epileptic and stroke patients. It is decreased in depressed patients and in patients with brain atrophy. As a neurotransmitter, aspartic acid may provide resistance to fatigue and thus lead to endurance, although the evidence to support this idea is not strong (Wikipedia). Aspartic acid supplements are being evaluated. Five grams can raise blood levels. Magnesium and zinc may be natural inhibitors of some of the actions of aspartic acid. Aspartic acid, when chemically coupled with the amino acid D-phenylalanine, is a part of a natural sweetener, aspartame. This sweetener is an advance in artificial sweeteners, and is probably safe in normal doses to all except phenylketonurics. Aspartic acid may be a significant immunostimulant of the thymus and can protect against some of the damaging effects of radiation. Aspartic acid is found in higher abundance in: oysters, luncheon meats, sausage meat, wild game, sprouting seeds, oat flakes, avocado, asparagus, young sugarcane, and molasses from sugar beets.

Maleic hydrazide is an odorless white solid. Sinks in water. (USCG, 1999) Maleic hydrazide is a pyridazinone. Maleic hydrazide (MH) was introduced into agriculture in the 1950s as a major commercial herbicide and a depressant of plant growth. It is a plant growth regulator (sprout inhibitor) and herbicide, that acts by inhibiting cell division in plants. It is used to control sprouting of potatoes and onions, suckers in tobacco, and growth of weeds, grasses and trees in/along lawns, turf, ornamental plants, non-bearing citrus, utility and highway rights-of-way, airports and industrial land. Most of the maleic hydrazide used in the U.S. is applied to tobacco (86-88%), followed by potatoes (10%), It is used to control sucker growth on tobacco plants, retardation of flowering and prolongation of dormancy period. 1,2-Dihydro-3,6-pyridazinedione. A herbicide and plant growth regulator; also used to control suckering of tobacco. Its residue in food and tobacco is highly toxic, causing CNS disturbances and liver damage.

2-Hydroxy-4-imino-2,5-cyclohexadienone is found in mushrooms. Red pigment found in the sporulating gill tissue of the mushroom Agaricus bisporus (button mushroom

Picolinic acid is a metabolite of the tryptophan catabolism. Picolinic acid is produced under inflammatory conditions and a costimulus with interferon-gamma (IFNgamma) of macrophage (Mphi) effector functions, is a selective inducer of the Mphi inflammatory protein-1alpha (MIP-1alpha) and -1beta (MIPs), two chemokines/cytokines involved in the elicitation of the inflammatory reactions and in the development of the Th1 responses. IFNgamma and picolinic acid have reciprocal effects on the production of MIPs chemokines and the expression of their receptor. The concerted action of IFNgamma and picolinic acid on MIP-1alpha/beta chemokine/receptor system is likely to be of pathophysiological significance and to represent an important regulatory mechanism for leukocyte recruitment and distribution into damaged tissues during inflammatory responses. Picolinic acid has an effect on the production of L-arginine-derived reactive nitrogen intermediates in macrophages, by augmenting IFN-gamma-induced NO2- production, and acts synergistically with IFN-gamma in activating macrophages. Children with acrodermatitis enteropathica (AE) are treated with oral zinc dipicolinate (zinc-PA). The concentration of picolinic acid in the plasma of asymptomatic children with AE was significantly less than that of normal children. However, oral treatment with PA alone is ineffective. The results support the hypothesis that the genetic defect in AE is in the tryptophan pathway, although the role of PA in zinc metabolism remains to be defined. (PMID:15206716, 8473748, 1701787, 6694049).

D-Aspartic acid is the D-isomer of aspartic acid. Since its discovery in invertebrates, free D-aspartate (D-Asp) has been identified in a variety of organisms, including microorganisms, plants, and lower animals, mammals and humans. D-Asp in mammalian tissues is present in specific cells, indicating the existence of specific molecular components that regulate D-Asp levels and localization in tissues. In the rat adrenal medulla, D-Asp is closely associated with adrenaline-cells (A-cells), which account for approximately 80% of the total number of chromaffin cells in the tissue, and which make and store adrenaline. D-Asp appears to be absent from noradrenaline-cells (NA-cells), which comprise approximately 20% of the total number of chromaffin cells in the adrenal medulla, and which make and store noradrenaline. D-aspartate oxidase (EC 1.4.3.1, D-AspO), which catalyzes oxidative deamination of D-Asp, appears to be present only in NA-cells, suggesting that the lack of D-Asp in these cells is due to D-Asp oxidase-mediated metabolism of D-Asp. In the rat adrenal cortex, the distribution of D-Asp changes during development. It has been suggested that developmental changes in the localization of D-Asp reflects the participation of D-Asp in the development and maturation of steroidogenesis in rat adrenal cortical cells. D-Asp is involved in steroid hormone synthesis and secretion in mammals as well. D-Asp is synthesized intracellularly, most likely by Asp racemase (EC 5.1.1.13). Endogenous D-Asp apparently has two different intracellular localization patterns: cytoplasmic and vesicular. D-Asp release can occur through three distinct pathways: 1) spontaneous, continuous release of cytoplasmic D-Asp, which is not associated with a specific stimulus; 2) release of cytoplasmic D-Asp via a volume-sensitive organic anion channel that connects the cytoplasm and extracellular space; 3) exocytotic discharge of vesicular D-Asp. D-Asp can be released via a mechanism that involves the L-Glu transporter. D-Asp is thus apparently in dynamic flux at the cellular level to carry out its physiological function(s) in mammals (PMID:16755369).

Sarcosine is the N-methyl derivative of glycine. Sarcosine is metabolized to glycine by the enzyme sarcosine dehydrogenase, while glycine-N-methyl transferase generates sarcosine from glycine. Sarcosine is a natural amino acid found in muscles and other body tissues. In the laboratory it may be synthesized from chloroacetic acid and methylamine. Sarcosine is naturally found in the metabolism of choline to glycine. Sarcosine is sweet to the taste and dissolves in water. It is used in manufacturing biodegradable surfactants and toothpastes as well as in other applications. Sarcosine is ubiquitous in biological materials and is present in such foods as egg yolks, turkey, ham, vegetables, legumes, etc. Sarcosine is formed from dietary intake of choline and from the metabolism of methionine, and is rapidly degraded to glycine. Sarcosine has no known toxicity, as evidenced by the lack of phenotypic manifestations of sarcosinemia, an inborn error of sarcosine metabolism. Sarcosinemia can result from severe folate deficiency because of the folate requirement for the conversion of sarcosine to glycine (Wikipedia). Sarcosine has recently been identified as a biomarker for invasive prostate cancer. It was found to be greatly increased during prostate cancer progression to metastasis and could be detected in urine. Sarcosine levels were also increased in invasive prostate cancer cell lines relative to benign prostate epithelial cells (PMID: 19212411).

2,3,4,5-Tetrahydro-2-pyridinecarboxylic acid (CAS: 3038-89-9), also known as 2,3,4,5-tetrahydropiperidine-2-carboxylate and 1-piperideine-6-carboxylic acid, is a cyclic intermediate in lysine degradation. L-Lysine is an essential amino acid that is a necessary building block for all protein in the body and It plays a major role in calcium absorption; building muscle protein; recovering from surgery or sports injuries; and the body's production of hormones, enzymes, and antibodies. In the lysine degradation pathway, 2,3,4,5-tetrahydro-2-pyridinecarboxylic acid is a substrate for L-aminoadipate-semialdehyde dehydrogenase (amaA) and can be formed by the spontaneous cyclization of 2-aminoadipate-6-semialdehyde. 2,3,4,5-Tetrahydro-2-pyridinecarboxylic acid is also an intermediate in glycine, serine, and threonine metabolism. It is a substrate for peroxisomal sarcosine oxidase.

An optically active form of penicillamine having D-configuration. Pharmaceutical form (L-form is toxic) of chelating agent used to treat heavy metal poisoning." []

A gamma-amino acid comprising that is GABA in which one of the hydrogens attached to the nitrogen is replaced by a methyl group." []

1-Piperideine-2-carboxylic acid (P2C), also known as Δ1-pipecolic acid, is classified as a member of the tetrahydropyridines. Tetrahydropyridines are derivatives of pyridine in which two double bonds in the pyridine moiety are reduced by adding four hydrogen atoms. 1-Piperideine-2-carboxylic acid is considered to be slightly soluble (in water) and acidic. 1-Piperideine-2-carboxylic acid is an intermediate of the L-lysine metabolic pathway in the brain; the uptake of P2C into the synaptosome of the cerebral cortex was Na+ and temperature-dependent (PMID: 7654748).

p-Aminobenzoic acid, also known as 4-aminobenzoic acid or PABA, is an organic compound with molecular formula C7H7NO2. PABA is a white crystalline substance that is only slightly soluble in water. It consists of a benzene ring substituted with an amino group and a carboxylic acid. PABA is an essential nutrient for some bacteria and is sometimes called vitamin Bx. However, PABA is not essential for humans and it varies in its activity from other B vitamins. PABA is sometimes marketed as an essential nutrient under the premise that it can stimulate intestinal bacteria. Certain bacteria in the human intestinal tract such as E. coli generate PABA from chorismate. Humans lack the enzymes to convert PABA into folate, and therefore require folate from dietary sources such as green leafy vegetables. Although some intestinal bacteria can synthesize folate from PABA and some E. coli can synthesize folate this requires six enzymatic activities in folate synthesis which are not all done in the same bacteria. PABA used to be a common sunscreen agent until it was found to also be a sensitizer. The potassium salt of PABA is used therapeutically in fibrotic skin disorders. PABA can also be found in Acetobacter (DOI: 10.3181/00379727-52-14147).

beta-Alanine is the only naturally occurring beta-amino acid - an amino acid in which the amino group is at the beta-position from the carboxylate group. It is formed in vivo by the degradation of dihydrouracil and carnosine. It is a component of the naturally occurring peptides carnosine and anserine and also of pantothenic acid (vitamin B-5), which itself is a component of coenzyme A. Under normal conditions, beta-alanine is metabolized into acetic acid. beta-Alanine can undergo a transanimation reaction with pyruvate to form malonate-semialdehyde and L-alanine. The malonate semialdehyde can then be converted into malonate via malonate-semialdehyde dehydrogenase. Malonate is then converted into malonyl-CoA and enter fatty acid biosynthesis. Since neuronal uptake and neuronal receptor sensitivity to beta-alanine have been demonstrated, beta-alanine may act as a false transmitter replacing gamma-aminobutyric acid. When present in sufficiently high levels, beta-alanine can act as a neurotoxin, a mitochondrial toxin, and a metabotoxin. A neurotoxin is a compound that damages the brain or nerve tissue. A mitochondrial toxin is a compound that damages mitochondria and reduces cellular respiration as well as oxidative phosphorylation. A metabotoxin is an endogenously produced metabolite that causes adverse health effects at chronically high levels. Chronically high levels of beta-alanine are associated with at least three inborn errors of metabolism, including GABA-transaminase deficiency, hyper-beta-alaninemia, and methylmalonate semialdehyde dehydrogenase deficiency. beta-Alanine is a central nervous system (CNS) depressant and is an inhibitor of GABA transaminase. The associated inhibition of GABA transaminase and displacement of GABA from CNS binding sites can also lead to GABAuria (high levels of GABA in the urine) and convulsions. In addition to its neurotoxicity, beta-alanine reduces cellular levels of taurine, which are required for normal respiratory chain function. Cellular taurine depletion is known to reduce respiratory function and elevate mitochondrial superoxide generation, which damages mitochondria and increases oxidative stress (PMID: 27023909). Individuals suffering from mitochondrial defects or mitochondrial toxicity typically develop neurotoxicity, hypotonia, respiratory distress, and cardiac failure. beta-Alanine is a biomarker for the consumption of meat, especially red meat.

Isoguvacine is a tetrahydropyridine.