Chitin synthase in Mortierella vinacea: properties, cellular location and synthesis in growing cultures

Chitin synthase of Mortierella vinacea was present in the "microsomal' fraction (100 000 g precipitate), the 'cell-wall' fraction (2000 g precipitate) and the 'mitochondrial' fraction (10 000 g precipitate). The properties of the 'microsomal' enzyme were investigated. The pH optimum was between 5-8 and 6-2, and the temperature optimum was between 31 and 33 degrees C. The Km for UDP N-acetyl-D-glucosamine was 1.8 mM. The enzyme was stimulated by Mg2+ and a slight stimulation was also effected by N-acetyl-D-glucosamine. Soluble chitodextrins were inhibitory. A pH-dependent, heat-stable inhibitor of chitin synthase activity was present in the soluble cytoplasm from the mycelium. The effects of aeration and glucose concentration on enzyme production in growing cultures were also investigated; maximum specific activity of chitin synthase was associated with the cessation of exponential growth.