ENZYMATIC STUDY ON FOLIC ACID BIOSYNTHESIS BY MYCOBACTERIUM AVIUM

Abstract

1. The pathway of folic acid biosynthesis by the enzyme extracted from Mycobacterium avium is found to be the following: PABA and L-glutamate couple together to form p-aminobenzoylglutamate, which is then coupled with xanthopterin to form folic acid.
2. From the experiments using the resin-treated enzyme which is almost free from coenzymes, the coupling reaction of PABA and L-glutamate, a kind of peptide formation, requires ATP, CoA and Mg⁺⁺ as cofactors, whereby pyrophosphoric acid and AMP are liberated equimolecularly.
3. The amount of p-aminobenzoyl hydroxamate formed in this reaction is not reduced even when CoA is removed by resin treatment. It was presumed from this and other reasons that p-aminobenzoyl-AMP and p-aminobenzoyl-CoA are the active intermediates of PABA.
4. A new method was devised for estimating folic acid alone applying the microbioassay using Streptocuccus faecalis to a fraction of Amberlite IR-4B. Using this method, folic acid was found to be synthesized from p-aminobenzoyl glutamate and xanthopterin.
5. The synthesizing enzyme of this step was found to be able to be divided into active apo-enzymes and co-enzymes by treatment with Amberlite IRA-400.