A Streptomyces-pQpsin inhibitor (S-PI or pepstatin Ac)-insensitive carboxyl proteinase was found in a still culture filtrate of Ganoderma lucidum (Manhen-take). The new carboxyl proteinase was purified, and about 15 mg of the purified enzyme was obtained from 15 liters of culture filtrate, with 13% recovery. The enzyme showed a single protein band on polyacrylamide gel electrophoresis.
The enzyme was most active at pH 3.2 toward hemoglobin, and at pH 2.0 toward casein, and stable only in the narrow pH range of 3.5 to 5.2 even under mild treatment (37°C for 3hr). The molecular weight and isoelectric point were 36, 000 and pH 5.3, respectively. The enzyme did not contain methionine.
The enzyme was characterized by the following points: (1) the proteolytic activity was not inhibited by carboxyl proteinase inhibitors such as S-PI, DAN, and EPNP; (2) the enzyme was very unstable; (3) the caseinolytic activity was very low compared with the hydrolysis of hemoglobin (about 15%); (4) the enzyme split preferentially the Phe(24)-Phe(25) bond of oxidized insulin Bchain at the rate of 50% for total hydrolysis. These characteristics were compared with the carboxyl proteinases isolated from Scytalidium lignicolum and Lentinus edodes, which were reported to be SPI-and DAN-insensitive carboxyl proteinases.

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