Properties and inhibition of Sclerotium rolfsii chitin synthetase

A chitin synthetase (CS) preparation was obtained from mycelium of the plant pathogen Sclerotium rolfsii and partially characterised. The CS activity was stimulated by N‐acetyl‐D‐glucosamine and magnesium cations with an optimum temperature of 30°C and an optimum pH of 6.4. The enzyme required proteolytic activation and so apparently existed in a zymogenic form. The fungal CS was strongly inhibited by the nucleoside‐peptide antibiotics polyoxin‐D and nikkomycin, and weakly inhibited by the terpenoyl benzimidazole, 1‐geranyl‐2‐methylbenzimidazole. It was insensitive to captan and to insecticidal benzoylphenyl ureas. Disrupted chitin formation caused by polyoxin‐D showed as swollen hyphae containing numerous depressions. The antibiotic also reduced formation of sclerotia and the few that did form were large, irregular in shape and light coloured.