Dairy Chemistry And Biochemistry

VITAMINS IN MILK AND DAIRY PRODUCTS 285

6.3,7 Folate

Folate consists of a substituted pteridine ring linked through a methylene
bridge to p-aminobenzoic acid and glutamic acid (6.31). Up to seven
glutamic acid residues can be attached by y-carboxyl linkages, producing
polyglutamyl folate (6.31) which is the major dietary and intracellular form
of the vitamin. Reductions and substitutions on the pteridine ring result in
tetrahydrofolate (H4 folate; 6.32) and 5-methyl tetrahydrofolate (5-methyl-
H, folate; 6.33). Folate is a co-factor in the enzyme-catalysed transfer of
single carbon atoms in many metabolic pathways, including the biosynthesis
of purines and pyramidines (essential for DNA and RNA) and interconver-
sions of amino acids. Folate interacts with vitamin B,, (section 6.3.8) in the
enzyme-catalysed synthesis of methionine and in the activation of 5-methyl-
H, folate to H, folate. H, Folate is involved in a complex and inter-linked
series of metabolic reactions (Garrow and James, 1993).

n

Folate

A

Tetrahydrofolate

H

5-methyl tetrahydrofolate