Enzymes from Escherichia coli synthesize o-succinylbenzoic acid, an intermediate in menaquinone (vitamin K2) biosynthesis.

Cell-free preparations have been obtained from Escherichia coli AN 154 which catalyze the conversion of chorismic acid and alpha-ketoglutaric acid to o-succinylbenzoic acid. This result constitutes the first experimental verification of the committed step in menaquinone biosynthesis. The enzymatic biosynthesis of o-succinylbenzoic acid was demonstrated in experiments utilizing [U-14C]alpha-ketoglutaric acid as substrate. Following purification of O-succinylbenzoic acid and conversion to the dimethyl derivative, the presence of 14C was shown by scanning of thin layer chromatograms, and by radiogas chromatography. Proof for the formation of o-succinylbenzoic acid was also obtained by combined gas chromatography/mass spectrometry. The formation of o-succinylbenzoic acid in these extracts required the presence of thiamin pyrophosphate; when this cofactor was omitted from the incubations, there was a substantial diminution in the incorporation of radioactivity from alpha-ketoglutarate into o-succinylbenzoic acid (from 4- to 8-fold). These results support the suggestion (Campbell, I. M. (1969) Tetrahedron Lett. 4777-4780) that the three-carbon unit of lawsone and, hence by inference, the four-carbon side chain of o-succinylbenzoic acid, is derived from the thiamin pyrophosphate adduct of succinic semialdehyde (likely in the anion form). The activated form of succinic semialdehyde is derived by the action of the first enzyme of the alpha-ketoglutarate dehydrogenase complex or by a similar decarboxylase enzyme.