Pyridoxine and related compounds vitamin

Vitamin Bg occurs naturally in three related forms pyridoxine (6.26 the alcohol form), pyridoxal (6.27 aldehyde) and pyridoxamine (6.28 amine). All are structurally related to pyridine. The active co-enzyme form of this vitamin is pyridoxal phosphate (PLP 6.29), which is a co-factor for transaminases which catalyse the transfer of amino groups (6.29). PLP is also important for amino acid decarboxylases and functions in the metabolism of glycogen and the synthesis of sphingolipids in the nervous system. In addition, PLP is involved in the formation of niacin from tryptophan (section 6.3.3) and in the initial synthesis of haem. 

Deficiency of vitamin Bg is characterized by weakness, irritability and insomnia and later by convulsions and impairment of growth, motor 

Since vitamin Bg is essential for amino acid (and hence protein) metabolism, its RDA is quoted in terms of protein intake (0.016 mg per g protein per day, equivalent to about 2.0 and 1.6 mg day for men and women. 

Whole milk contains, on average, 0.06 mg Bg per 100 g, mainly in the form of pyridoxal (80%) the balance is mainly pyridoxamine (20%), with trace amounts of pyridoxamine phosphate. Concentrations in raw ovine and pasteurized caprine milks are similar to those in cows milk (0.08 and 0.06 mg per 100 g, respectively). The concentration of Bg varies during lactation colostum contains lower levels than mature milk. Seasonal variation in the concentration of vitamin Bg has been reported in Finnish milk levels were higher (14%) when cattle were fed outdoors than when they were fed indoors. Mature human milk contains about 0.01 mg Bg per 100 g. 

In general, dairy products are not major sources of Bg in the diet. Concentrations in cheeses and related products vary from about 0.04 (fromage frais, cream cheese) to 0.22 (Camembert) mg per 100 g (Appendix 6A). Whole-milk yogurt contains roughly 0.1 mg per 100 g and the concentration in skim-milk powder is c. 0.6 mg per 100 g. 

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