A comparative study of properties of chitin synthase from two Mortierella species

Abstract

Properties of chitin synthase obtained from mycelial homogenates of Mortierella pusilla and Mortierella candelabrum were compared. The enzyme was localized mainly in the mixed membrane fractions of both species. The reaction product, chitin, was characterized by its insolubility in weak acid and alkali and by the release of glucosamine and diacetylchitobiose on hydrolysis with strong acid and chitinase, respectively. Apparent Km values for UDP-N-acetyl-D-glucosamine (UDP-GlcNAc) were 1.8 mM and 2.0 mM for M. pusilla and M. candelabrum, respectively, and the inhibition constant, Ki, for polyoxin D was three orders of magnitude lower than the Km for UDP-GlcNAc. Enzyme preparations from both species were stimulated by Mg2+, Mn2+ or Co2+ and N-acetyl-glucosamine. Large differences in the ratio of active to inactive chitin synthase of the two species, were observed. Unlike M. candelabrum chitin synthase activity in the membrane fraction of M. pusilla increased during low temperature storage. The 100 000 × g supernatant fractions from cell-free extracts of M. candelabrum and M. pusilla were found to inhibit chitin synthase activity in both the fungi.