Biosynthesis of o-succinylbenzoic acid. I: Cell free synthesis of o-succinylbenzoic acid from isochorismic acid in enzyme preparations from vitamin K producing bacteria.

Escherichia coli K12 and a mutant of E. coli (viz., AN 154) as well as Aerobacter aerogenes 62-1 (i.e., Klebsiella pneumoniae) were used as sources of the enzyme catalyzing the formation of o-succinylbenzoic acid (OSB) from isochorismic acid and alpha-ketoglutaric acid in the presence of thiamine pyrophosphate. The product of the reaction (OSB) was identified by HPLC before and after derivatization to the methylester, dilactone, and coenzyme A ester. OSB synthase and alpha-ketoglutarate dehydrogenase are similar in that both decarboxylate alpha-ketoglutarate in the presence of thiamine pyrophosphate but the enzyme systems can be separated easily by several methods. Reexamination of mutants E. coli AN 154 and AN 191 showed that these mutants are leaky, rather than blocked, between chorismic acid and isochorismic acid. This finding, together with the observation that isochorismic acid rather than chorismic acid is the substrate of OSB synthase, invalidates previous assumptions on the reaction initiating vitamin K2 biosynthesis.