Studies on the Mode of Action of Polyoxins

Abstract

(1) Chitin-UDP acetylglucosaminyltransferase (E.C. 2.4.1.16., chitin synthetase) in the cell-free system from phytopathogenic fungus Piricularia oryzae, and effects of various polyoxins and related compounds on the enzyme activity were studied. Polyoxins A~M, polyoxin A derivatives, polyoxin C derivatives, 5′-amino-5′-deoxyuridine, uridine and thymidine inhibited equally the incorporation of N-acetylglucosamine (GlcNAc) from UDP-N-acetylglucosamine (UDP-GlcNAc) into chitin.(2) Competition between the above inhibitors and UDP-GlcNAc was observed by kinetic studies. The Km for UDP-GlcNAc was determined to be 3.3 × 10−3 m and the Ki values for polyoxins A~M, except polyoxin C, were found to be in the range of 3.3 × 10−5 m to 3.4 × 10−6 m. For polyoxin C, 5′-amino-5′-deoxyuridine and uridine, the Ki values of 2.7 × 10−3 m, 8.0 × 10−3 m and 3.0 × 10−3 m were given, respectively. The inhibitor constants for other related compounds were also calculated.(3) The values of binding affinity, −ΔG, for formation of su...