Answer to Question #86880 in Biochemistry for Arun Rawat

Question #86880
b) Give the role of following vitamins in biochemical reactions. Explain with the help of an example.
i) Thiamine ii) Pyridoxine iii) Riboflavin
Expert's answer

Thiamine (vitamin B1) diphosphate serves as a coenzyme in reactions of the cleavage of bonds between carbon atoms - oxidative decarboxylation of alpha-keto acids (pyruvate, alpha-ketoglutaric, and alpha-keto acids, formed during the decomposition of leucine, isoleucine, and valine), as well as the transketolase reaction of pentoses. For example, during the decarboxylation of pyruvic acid using pyruvate decarboxylase, acetaldehyde is formed, which is converted into ethanol under the influence of alcohol dehydrogenase. TPP is an essential cofactor of pyruvate decarboxylase. 

Pyridoxine (vitamin B6) is a water-soluble vitamin that is involved in the synthesis and breakdown of amino acids. The active form of pyridoxine is pyridoxal-5-phosphate that is the most important coenzyme in the metabolism of amino acids. Pyridoxal phosphate is also part of glycogen phosphorylase, which is involved in the breakdown of glycogen. Pyridoxine promotes the transfer of amino groups and carboxyl groups in amino acid metabolism reactions. It is used as a coenzyme in aminotransferases that transfer amino groups between amino acids and keto acids (for example, alanine-pyruvic acid, alpha-ketoglutaric acid-glutamic acid), and also as a coenzyme of decarboxylase, involved in the synthesis of biogenic amines from amino acids including serotonin, glutamic acid, gamma-aminobutyric acid (GABA), histamine.

Riboflavin (vitamin B2) is a water-soluble vitamin synthesized by plants and microorganisms. Vitamin B2 is a part of the flavin coenzymes –FMN and FAD, which are intermediate carriers of electrons and protons in the respiratory chain and coenzymes oxidase. Also, FAD is a coenzyme of pyruvate and α-ketoglutarate dehydrogenase complexes and participates in fatty acid oxidation reactions in mitochondria

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