Properties of a specific protease for pyridoxal enzymes and its biological role.

A new protease which specifically acts on the apo-form of pyridoxal enzymes was discovered in rat small intestine and skeletal muscle. This enzyme was puriCed about SM-fold from the small intestine of vitamin Be-deficient rats. Some proporties of the enzyme and its action were studied. The enzyme split the apo-protein of ornithine transaminase into two products, a homogeneous smaller protein and an oligopeptide, and thereby inactivated the transaminase. The substrate enzyme, omithine transaminase, and the larger product have a$,,,, values of 9.9 and 5.1, respectively. The enzyme inactivated all of the apo-pyridoxal enzymes tested, including serine dehydratase, ornithine transaminase, tyrosine transaminase and aspartate transaminase, but did not affect non-pyridoxal enzymes (glutamic dehydrogenase, lactic dehydrogenase, urease, and glutaminase), bovine serum albumin or some synthetic substrates. Addition of pyridoxal phosphate or a high concentration of pyridoxal had a protective effect against the specific protease, but another active coenzyme, pyridoxamine phosphate, did not. The activity of this protease in the small intestine increased during vitamin Be deficiency. A reciprocal relation was found between the activity of this protease and that of ornithine transaminase in the small intestine.