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Abstract
SUMMARY: The solubilized chitin synthetase preparation from the stipes of Coprinus cinereus is activated by its substrate, UDP-N-acetylglucosamine, and by carbohydrates, in particular N-acetylglucosamine, diacetylchitobiose and glucose. Analysis of the results of variation in enzyme activity with UDP-GlcNAc concentration by several methods suggested that this substrate is an allosteric activator, with Hill coefficients close to 2 and 4 at concentrations above and below 0·1 mm respectively, and an [S]0·5 value of 0·9 mm. N-acetylglucosamine lessened but did not abolish the sigmoidal shape of the velocity-substrate concentration plot. The chitin synthetase was inhibited by adenine and uridine nucleotides, and uridine diphosphate was a powerful competitive inhibitor. The enzyme preparation also contained a nucleoside diphosphatase activity and the implications of the removal of the inhibitory UDP formed by the chitin synthetase are considered.
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