Menaquinone (vitamin K2) biosynthesis: Conversion of o-succinylbenzoic acid to 1,4-dihydroxy-2-naphthoic acid by Mycobacterium phlei enzymes

Abstract

The coenzyme A (CoA) and adenosine 5'-triphosphate-dependent conversion of o-succinylbenzoic acid (4-[2'-carboxyphenyl]-4-oxobutyric acid) to 1,4-dihydroxy-2-naphthoic acid is an important step in menaquinone (vitamin K2) biosynthesis. Cell-free extracts catalyzing this conversion, obtained from M. phlei, were separated into three protein fractions by treatment with protamine sulfate. The second fraction (fraction B) and the supernatant (fraction S) alone did not catalyze dihydroxynaphthoate formation, but did so in combination. All of the results were consistent with the formation of an unstable intermediate, likely an o-succinylbenzoyl-CoA compound, by the action of fraction S. Adenosine 5'-triphosphate was required in this reaction and adenosine 5'-monophosphate was formed. This enzyme activity was termed o-succinylbenzoyl-CoA synthetase: the enzyme showed a marked stability to 0.1 N hydrochloric acid. The presumed o-succinylbenzoyl-CoA derivative was rather unstable; under a variety of conditions, it was converted to a spirodilactone form of o-succinylbenzoate. Fraction B contained an enzyme, termed naphthoate synthase, which converted to o-succinylbenzoyl-CoA derivative to 1,4-dihydroxy-2-naphthoate.