Chitin synthase of Apodachlya sp.

Abstract

Chitin synthase activity was demonstrated in preparations of Apodachlya sp. which incorporated radioactivity from UDP- N-acetyl- d-[U- 14C]glucosamine into insoluble product. The labeled product yielded d-[ 14C]glucosamine after acid hydrolysis and N-acetyl- d-[ 14C]glucosamine upon treatment with chitinase. The enzyme was inhibited by polyoxin D and, in crude homogenates, activated by trypsin. Activity was primarily localized in the mixed membrane fraction (74, 000 g pellet) of Apodachlya sp. homogenates and was partially solubilized from this particulate preparation by digitonin treatment but not by zwitterionic detergents. Notably, digitonin treatment caused a fivefold increase in total activity, distributed between sedimentable (74, 000 g) and nonsedimentable fractions. Trypsin activation was not observed with 74, 000 g sedimentable activity (either before or after digitonin treatment) or digitonin-solubilized activity. Enzyme properties were similar in particulate and soluble preparations. Optimum enzyme activity occurred between pH 7.5 and 8.5, at approximately 42 to 46°C. Magnesium or manganese was required for enzyme activity, while cobalt, calcium, and iron did not markedly affect activity, and copper and zinc were strong inhibitors. N-Acetyl- d-glucosamine slightly increased enzyme activity.