Chitinase activity in germinating cells of Mucor rouxii

Chitinase activity in germinating cells (4 h cultures) of Mucor rouxii was studied. The enzyme activity was recovered in a high speed supernatant of cell homogenates. No activity was detected in the mixed membrane fraction or in the cell walls. Maximum activity was observed at pH 7.6 and at 30-35 degrees C using the chromogenic assay with chitin azure. The latter was digested by GS-chitinase in a manner dependent on substrate concentration and time of incubation. As with other chitinases, GS-chitinase was much more effective against nascent than against preformed chitin. The main product of nascent chitin digestion was diacetylchitobiose, although significant amounts of the trimer were also detected in the hydrolyzates. Allosamidin, an insect and fungal chitinase inhibitor, strongly inhibited hydrolysis of nascent chitin but not of chitin azure by GS-chitinase. The drug failed to inhibit the germination and the ensuing growth of the fungus. Results are discussed in terms of the possible role of GS-chitinase in germination.