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Malic acid (CAS: 6915-15-7) is a tart-tasting organic dicarboxylic acid that plays a role in many sour or tart foods. Apples contain malic acid, which contributes to the sourness of a green apple. Malic acid can make a wine taste tart, although the amount decreases with increasing fruit ripeness (Wikipedia). In its ionized form, malic acid is called malate. Malate is an intermediate of the TCA cycle along with fumarate. It can also be formed from pyruvate as one of the anaplerotic reactions. In humans, malic acid is both derived from food sources and synthesized in the body through the citric acid cycle or Krebs cycle which takes place in the mitochondria. Malate's importance to the production of energy in the body during both aerobic and anaerobic conditions is well established. Under aerobic conditions, the oxidation of malate to oxaloacetate provides reducing equivalents to the mitochondria through the malate-aspartate redox shuttle. During anaerobic conditions, where a buildup of excess reducing equivalents inhibits glycolysis, malic acid's simultaneous reduction to succinate and oxidation to oxaloacetate is capable of removing the accumulating reducing equivalents. This allows malic acid to reverse hypoxia's inhibition of glycolysis and energy production. In studies on rats, it has been found that only tissue malate is depleted following exhaustive physical activity. Other key metabolites from the citric acid cycle needed for energy production were found to be unchanged. Because of this, a deficiency of malic acid has been hypothesized to be a major cause of physical exhaustion. Notably, the administration of malic acid to rats has been shown to elevate mitochondrial malate and increase mitochondrial respiration and energy production. Malic acid has been found to be a metabolite in Aspergillus (Hugo Vanden Bossche, D.W.R. Mackenzie and G. Cauwenbergh. Aspergillus and Aspergillosis, 1987).

D-Malic acid is found in herbs and spices. This enantiomer of rare occurrence; reported from fruits and leaves of Hibiscus sabdariffa (roselle) although there are many more isolations of malic acid with no opt. rotn. given and some may be of the R-for

A 2-hydroxydicarboxylic acid that is succinic acid in which one of the hydrogens attached to a carbon is replaced by a hydroxy group." []

The 3-dehydro derivative of L-threonic acid." []

A ketoaldonic acid that is butyric acid carrying an oxo substituent at position 3 as well as two hydroxy substituents at positions 2 and 4 (the S-enantiomer)." []

Asparagine (Asn) or L-asparagine 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-asparagine is one of 20 proteinogenic amino acids, i.e., the amino acids used in the biosynthesis of proteins. Asparagine is found in all organisms ranging from bacteria to plants to animals. In humans, asparagine is not an essential amino acid, which means that it can be synthesized from central metabolic pathway intermediates in humans and is not required in the diet. The precursor to asparagine is oxaloacetate. Oxaloacetate is converted to aspartate using a transaminase enzyme. This enzyme transfers the amino group from glutamate to oxaloacetate producing alpha-ketoglutarate and aspartate. The enzyme asparagine synthetase produces asparagine, AMP, glutamate, and pyrophosphate from aspartate, glutamine, and ATP. In the asparagine synthetase reaction, ATP is used to activate aspartate, forming beta-aspartyl-AMP. Glutamine donates an ammonium group which reacts with beta-aspartyl-AMP to form asparagine and free AMP. Since the asparagine side chain can make efficient hydrogen bond interactions with the peptide backbone, asparagines are often found near the beginning and end of alpha-helices, and in turn motifs in beta sheets. Its role can be thought as "capping" the hydrogen bond interactions which would otherwise need to be satisfied by the polypeptide backbone. Asparagine also provides key sites for N-linked glycosylation, a modification of the protein chain that is characterized by the addition of carbohydrate chains. A reaction between asparagine and reducing sugars or reactive carbonyls produces acrylamide (acrylic amide) in food when heated to sufficient temperature (i.e. baking). These occur primarily in baked goods such as French fries, potato chips, and roasted coffee. Asparagine was first isolated in 1806 from asparagus juice --hence its name. Asparagine was the first amino acid to be isolated. The smell observed in the urine of some individuals after the consumption of asparagus is attributed to a byproduct of the metabolic breakdown of asparagine, asparagine-amino-succinic-acid monoamide. However, some scientists disagree and implicate other substances in the smell, especially methanethiol.

Glyoxylic acid or oxoacetic acid is an organic compound that is both an aldehyde and a carboxylic acid. Glyoxylic acid is a liquid with a melting point of -93°C and a boiling point of 111°C. It is an intermediate of the glyoxylate cycle, which enables certain organisms to convert fatty acids into carbohydrates. The conjugate base of glyoxylic acid is known as glyoxylate (PMID: 16396466). In humans, glyoxylate is produced via two pathways: (1) through the oxidation of glycolate in peroxisomes and (2) through the catabolism of hydroxyproline in mitochondria. In the peroxisomes, glyoxylate is converted into glycine by glyoxylate aminotransferase (AGT1) or into oxalate by glycolate oxidase. In the mitochondria, glyoxylate is converted into glycine by mitochondrial glyoxylate aminotransferase AGT2 or into glycolate by glycolate reductase. A small amount of glyoxylate is converted into oxalate by cytoplasmic lactate dehydrogenase. Glyoxylic acid is found to be associated with primary hyperoxaluria I, which is an inborn error of metabolism. Under certain circumstances, glyoxylate can be a nephrotoxin and a metabotoxin. A nephrotoxin is a compound that causes damage to the kidney and kidney tissues. A metabotoxin is an endogenously produced metabolite that causes adverse health effects at chronically high levels. High levels of glyoxylate are involved in the development of hyperoxaluria, a key cause of nephrolithiasis (commonly known as kidney stones). Glyoxylate is both a substrate and inductor of sulfate anion transporter-1 (SAT-1), a gene responsible for oxalate transportation, allowing it to increase SAT-1 mRNA expression, and as a result oxalate efflux from the cell. The increased oxalate release allows the buildup of calcium oxalate in the urine, and thus the eventual formation of kidney stones. As an aldehyde, glyoxylate is also highly reactive and will modify proteins to form advanced glycation products (AGEs).

An alpha-amino acid in which one of the hydrogens attached to the alpha-carbon of glycine is substituted by a 2-amino-2-oxoethyl group." []

Animal and poultry feed additive.

THTC is a member of tetrahydrothiophenes.

D-Asparagine, also known as DSG, belongs to the class of organic compounds known as asparagine and derivatives. D-Asparagome is a non-essential amino acid that is involved in the metabolic control of cell functions in nerve and brain tissue. Asparagine and derivatives are compounds containing asparagine or a derivative thereof resulting from reaction of asparagine at the amino group or the carboxy group, or from the replacement of any hydrogen of glycine by a heteroatom. It is codified by the codons AAU and AAC. It is biosynthesized from Aspartic acid and Ammonia by asparagine synthetase.

BBT

1-benzothiophene is a benzothiophene and a member of 1-benzothiophenes.

A deoxypentose that is aldehydo-D-ribose in which the hydroxy group at position 5 is substituted by a hydrogen." []

Tetrahydro-2-methyl-2-thiophenethiol is a component of cooked meat aroma model systems.

D-Xylulose (CAS: 551-84-8) is a monosaccharide containing five carbon atoms. D-Xylulose is converted from xylitol by the enzyme NAD+-linked xylitol dehydrogenase (EC 1.1.1.9) in the glucuronate pathway, the most important xylitol-handling metabolic pathway in mammals. This activity has been described in human erythrocytes. Most likely, D-xylulose (as well as D-arabinose or D-ribulose) is a precursor of the pentiol D-arabitol, since pentitols are derived from their corresponding pentose phosphate precursors via pentoses. This pathway can play a role in inherited metabolic disorders underlying the accumulation of pentitols (e.g. ribose 5-phosphate isomerase deficiency and transaldolase deficiency). Although pentitols are present in all living organisms, knowledge concerning their metabolism is limited (PMID:15234337, Mol Genet Metab. 2004 Jul;82(3):231-7.).

(R) 2,3-Dihydroxy-isovalerate is an intermediate in valine, leucine and isoleucine biosynthesis. The pathway of valine biosynthesis is a four-step pathway that shares all of its steps with the parallel pathway of isoleucine biosynthesis. These entwined pathways are part of the superpathway of leucine, valine, and isoleucine biosynthesis , that generates not only isoleucine and valine, but also leucine. (R) 2,3-Dihydroxy-isovalerate is generated from 3-Hydroxy-3-methyl-2-oxobutanoic acid via the enzyme ketol-acid reductoisomerase (EC 1.1.1.86) then it is converted to 2-Oxoisovalerate via the dihydroxy-acid dehydratase (EC:4.2.1.9).

A dihydroxy monocarboxylic acid that is isovaleric acid which is substituted by hydroxy groups at positions 2 and 3." []

L-Ribulose (CAS: 2042-27-5) is a ketopentose - a monosaccharide containing five carbon atoms, including a ketone functional group. It has the chemical formula C5H10O5.

Zwitterionic form of L-asparagine arising from transfer of a proton from the carboxy to the amino group; major species at pH 7.3." []

2,3-Dihydroxyvaleric acid (DHVA) belongs to the class of organic compounds known as hydroxy fatty acids. These are fatty acids in which the chain bears a hydroxyl group. This compound has been detected in extracts from the purple carrot (https://doi.org/10.3390/app10238493). It is likely a hydroxylation derivative of the more common 2-hydroxyvaleric acid (an algal metabolite derived from a valeric acid) or 3-hydroxyvaleric acid (a 5-carbon ketone body made from odd carbon fatty acids in the liver). Very little is known about the origin of this particular hydroxy fatty acid.

Ureidopropionic acid, also known as 3-ureidopropanoate or N-carbamoyl-beta-alanine, belongs to the class of organic compounds known as ureas. Ureas are compounds containing two amine groups joined by a carbonyl (C=O) functional group. Ureidopropionic acid is an intermediate in the metabolism of uracil. More specifically, it is a breakdown product of dihydrouracil and is produced by the enzyme dihydropyrimidase. It is further decomposed into beta-alanine via the enzyme beta-ureidopropionase. Ureidopropionic acid is essentially a urea derivative of beta-alanine. High levels of ureidopropionic acid are found in individuals with beta-ureidopropionase (UP) deficiency (PMID: 11675655). Enzyme deficiencies in pyrimidine metabolism are associated with a risk for severe toxicity against the antineoplastic agent 5-fluorouracil. Ureidopropionic acid has been detected, but not quantified in, several different foods, such as gram beans, broccoli, climbing beans, oriental wheat, and mandarin orange (clementine, tangerine). This could make ureidopropionic acid a potential biomarker for the consumption of these foods.

3,3-Dimethyl-1,2-dithiolane is found in coffee and coffee products. 3,3-Dimethyl-1,2-dithiolane is detected in aroma of coffee.

A 4-oxo monocarboxylic acid that is 4-oxobutanoic acid which is substituted by a hydroxymethyl group at position 2." []

Deoxyribose is an aldopentose, a monosaccharide containing five carbon atoms, and including an aldehyde functional group. It is derived from the pentose sugar ribose by the replacement of the hydroxyl group at the 2 position with hydrogen, leading to the net loss of an oxygen atom, and has chemical formula C5H10O4. In deoxyribose, the carbon furthest from the attached carbon is stripped of the oxygen atom in what would be a hydroxyl group in ribose. The common base adenine (a purine derivative) coupled to deoxyribose is called deoxyadenosine. The 5-triphosphate derivative of adenosine, commonly called adenosine triphosphate (ATP) is an important energy transport molecule in cells. -- Wikipedia.