Pyruvoyl-dependent histidine decarboxylases. Mechanism of cleavage of the proenzyme from Lactobacillus buchneri.

When Lactobacillus buchneri was grown in the presence of [hydroxyl-18O]serine and pyridoxamine, no 18O was found in its histidine decarboxylase (HisDCase). However, when pyridoxamine was omitted from the growth medium, the labeled serine was incorporated into the HisDCase without dilution. Internal serine residues of the enzyme contained 18O only in their hydroxyl group, while the COOH-terminal serine of the beta chain of HisDCase contained equal amounts of 18O in both its hydroxyl and carboxyl group. This enzyme, like the HisDCase from Lactobacillus 30a (Recsei, P. A., Huynh, Q. K., and Snell, E. E. (1983) Proc. Natl. Acad. Sci. U.S.A. 80, 973-977), therefore, arises by nonhydrolytic serinolysis of its proenzyme. This result, together with comparative sequence data (Huynh, Q. K., and Snell, E. E. (1985) J. Biol. Chem. 260, 2798-2803), makes it highly probable that all of the pyruvoyl-dependent HisDCases arise by a similar mechanism from inactive proenzymes.