Novel characteristics of Selenomonas ruminantium lysine decarboxylase capable of decarboxylating both L-lysine and L-ornithine.

Lysine decarboxylase (LDC; EC 4.1.1.18) of Selenomonas ruminantium is a constitutive enzyme and is involved in the synthesis of cadaverine, which is an essential constituent of the peptidoglycan for normal cell growth. We purified the S. ruminantium LDC by an improved method including hydrophobic chromatography and studied the fine characteristics of the enzyme. Kinetic study of LDC showed that S. ruminantium LDC decarboxylated both L-lysine and L-ornithine with similar Km and the decarboxylase activities towards both substrates were competitively and irreversibly inhibited by DL-alpha-difluoromethylornithine, which is a specific inhibitor of ornithine decarboxylase (EC 4.1.1.17). We also showed a drastic descent of LDC activity owing to the degradation of LDC at entry into the stationary phase of cell growth.