Glutathione-independent isomerization of maleylpyruvate by Bacillus megaterium and other gram-positive bacteria.

Maleylpyruvate, the ring fission product of gentisic acid, was found to be isomerized to fumarylpyruvate without a requirement for glutathione by an enzyme activity found in cell extracts of m-hydroxybenzoate-grown Bacillus megaterium 410. The isomerization reaction was detected as a shift in the absorbance maximum from 330 nm, the maximum for maleylpyruvate, to 345 nm, the maximum for fumarylpyruvate, when assayed at pH 8.0. Ammonium sulfate precipitation and dialysis of B. megaterium cell extracts resolved the isomerase activity from low-molecular-weight compounds such as glutathione but did not eliminate the isomerase activity. Iodoacetate and p-chloromercuribenzoate were potent inhibitors of the isomerase from B. megaterium. However, N-ethylmaleimide and iodoacetamide did not significantly inhibit this activity. In addition, fumaric acid was demonstrated as a product of gentisate oxidation by dialyzed cell extracts of B. megaterium. Glutathione-independent maleylpyruvate isomerases with properties similar to the isomerase found in B. megaterium were also found in other genera of gram-positive organisms. Eleven different organisms representing the genera Bacillus, Arthrobacter, Corynebacterium, Nocardia, and Rhodococcus were all found to possess this novel type of glutathione-independent maleylpyruvate isomerase.