| Summary: | Chitin synthetase has been characterized from stipes of the toadstool Coprinns cinereus. This enzyme makes chitin, a major component of the walls of many fungi. It is probably associated with the plasmalemma and can be solubilized from a microsomal preparation by treatment with 10 mg/ml digitonin. This treatment results in a large increase in stability of the enzyme. The enzyme requires only magnesium ions and UDP-N-acetyl-glucosamine for activity and it is assumed that any primer required is firmly bound to the enzyme molecules. Glucose, N-acetylglucosamine and diacetylchitobiose activate chitin synthetase, while adenine and uridine nucleotides are inhibitory. The enzyme product UDP and the antibiotic polyoxin D are competitive inhibitors. Kinetic studies of the variation of activity with UDP-N-acetylglucosamine concentration suggest that this substrate is an allosteric activator of chitin synthetase, and the properties of the enzyme are related to various standard models of allosteric enzymes and to the responses of effectors present in vivo. The solubilized chitin synthetase preparation also contains proteolytic and nucleoside phosphatase activities. The properties of the uridine diphosphatase are examined for its effect on chitin synthetase through the enzyme product UDP. The enzyme is partially purified by ammonium sulphate precipitation, ion exchange chromatography and molecular exclusion chromatography. In these preparations the enzyme exists as aggregates of molecular weights of several millions which break down in the presence of salt. When eluted with 0.2 M-NaCl the enzyme anpears as a single peak with a molecular weight of about 150,000.
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