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10.1.4 Vitamin B6
Vitamin B6, consists of three closely related pyridine derivatives: pyridoxine, pyridoxal, and pyridoxamine and their corresponding phosphates. Of these, pyridoxine, pyridoxal phosphate, and pyridoxamine phosphate are the main representatives of the vitamin in the diet. All three have equal vitamin activity, as they can be interconverted in the body.
Functions: Pyridoxal phosphate is the coenzyme of several enzymes of amino acid metabolism. It functions by entering into a Schiff base combination between its aldehyde group and the amino group of an alpha-amino acid. Pyridoxal phosphate can facilitate changes in the three remaining bonds of the a-amino carbon to allow either transamination, decarboxylation, or threonine aldolase activity respectively.
Pyridoxal phosphate is involved in Glycogenolysis. The coenzyme is an integral part of the mechanisms of action of phosphorylase, the enzyme mediating the breakdown of glycogen. In this action, it also forms an initial Schiff base with an amino group of a lysine residue of the enzyme, which, however, remains intact throughout the phosphorolysis of the 1-4 glycosidic bond to form glucose 1-phosphate.
Deficiency: Deficiency of vitamin B6 is rare since it is available in most foods. Deficiency gives rise to irritability and depression. Infants fed on milk powders deficient in vitamin B6 were found to suffer from convulsions but responded rapidly to treatment with the vitamin. Alcoholics may also be deficient due to metabolism of ethanol to acetaldehyde which stimulates hydrolysis of the phosphate group of the coenzyme. RDA
Infants :0.3mg Children :0.6-1.2mg Adult (male) :1.6-2.0mg Adult (female) :1.6-2.0mg Pregnant women :2.5mg Lactating women :2.5mg
Sources Good sources: Milk, meat, liver and green leafy vegetables Fair sources : fish, eggs, fruits and vegetables. |