Chitinase activities were detected in the supernatant and microsomal fractions from homogenized mycelium of surface-grown cultures of Mucor mucedo. Most properties of the two preparations were very similar, e.g. pH optima were 5.65 and 5-55, respectively, and K , values were 16.7 and 19.2 mg chitin ml-l, respectively. Neither activity had a cationic requirement, but both were inhibited by Cu2+. Some properties differed. On freezing, the supernatant activity remained constant over 4 d and then gradually decreased, whereas microsomal activity increased, suggesting that endogenous activation was occurring. Prolonged incubations at 30 "C also allowed endogenous activation of microsomal activity, which could be prevented by incubation with phenylmethanesulphonyl fluoride. This enzyme activity could also be activated by treatment of the microsomes with proteases such as trypsin. Inactivation occurred after treatment with phospholipases, suggesting that microsomal chitinase requires phospholipidenzyme interactions for activity. Thus the microsomal activity behaved as a membrane-bound zymogen.

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