Isolation, partial purification, and some properties of protease I from a thermophilic mold Thermoascus aurantiacus var. levisporus

Abstract

When the thermophilic mold Thermoascus aurantiacus var. levisporus was grown in a modified Czapek Dox medium containing casein the filtrate was found to contain proteolytic activity. The maximum production of activity occurred at 50 ° C in a medium containing 8% casein. The filtrate was subjected to ammonium sulfate fractionation and chromatography on DEAE-cellulose. Two proteases were separated. No further work was done on protease II. Protease I was further purified by gel filtration on Sephadex G 100–200. It showed a 40-fold purification with a final recovery of approximately 25%. It is a neutral protease with a pH optimum at 7.0. The optimal activity of the enzyme occurred in 0.02 M phosphate buffer but was completely inhibited at a concentration of 0.1 M. The optimum temperature for casein hydrolysis was found to be 55 ° C. The enzyme was inhibited by Hg++ but was greatly stimulated by Cu++ and mercaptoethanol. Metallo and sulfhydryl agents had no significant effect on enzyme activity.