Abstract
A β‐glucan synthetase was isolated from a membrane fraction of the crayfish parasitic fungus Aphanomyces astaci Schikora, strain Si. [14C]‐UDP‐glucose was incorporated linearly for about 1 h at 30°C into an acid insoluble product. The apparent Km for UDP‐glucose was found to be approximately 4.5 mM and the apparent Ki for UDP, a competitive inhibitor of the reaction, was 1 mM. The acid insoluble product obtained after incubating this glucan synthetase with[14C]‐UDP‐glucose was partially characterized by glucanase treatment. This product mainly consisted of β‐1,3‐linked glucosyl units. Synthetase activity was not stimulated by MgCl2, but cellobiose as well as GTP and EDTA in combination or ATP alone enhanced enzyme activity. A high proportion of the A. astaci synthetase was probably already activated during preparation and not accessible to further stimulation by nucleotide additions as found for glucan synthetase of Saccharomyces cerevisiae and Candida albicans. No synthetase activity or any factors affecting this enzyme was present in the cytosol. An exudate prepared from the cuticle of the crayfish host, did not inhibit glucan synthetase activity in vitro.
Published Version
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