Dehydrogenase, from PenieiMum citrinum

A se}ectiye inactivating enzyme for the m-subunit of lactate dehydrogenase (LDH) was found in the cutture filtrate of PenieiM"m citrinum KE-1, newly isolated from soil. The enzyme was purified from the culture filtrate by ammonium sulfate fractionation, column chromatography on CM-Sepharose CL-6B, and gel filtration on Sephadex G-1OO. The purification was 124-fold with an activity yield of 81%. The purified enzyme gave a singte band, corresponding to a molecular weight of 32,OOO, on SDS polyacrylamide gel electrophoresis, and the isoelectric point was 9.5. The enzyme specifically inactivated the m-subunit of LDH but showed no actiyity on the h-subunit of LDH. The enzyme, named KE-1 proteinase, proved to be a serine-type proteinase. Limited proteolysis of natiye m-subunit of LDH was assumed to result ifl a loss ef