SOME CITRUS CHITINASES ALSO POSSESS CHITOSANASE ACTIVITIES

Several acidic chitinase and chitosanase isoforms were found in 4-week -old nonembryogenic sweet orange ('Valencia' [Citrus sinensis (L.) Osb eck]) callus tissue. Two isoforms (designated A1-CF1 and A1-CF2) were purified to homogeneity using HPLC size exclusion, anion exchange, and chromatofocusing techniques. Both hydrolase isoforms exhibited activi ty with either colloidal chitin or solubilized shrimp shell chitosan. Specific activities for the purified isoforms could not be calculated because of the lack of protein and contamination of ampholytes. Howeve r, the specific activities for chitinase and chitosanase after anion e xchange were respectively 404 nmol GlcNAc per min per mg protein and 2 ,475 nmol GlcN per min per mg protein. The M(r) for both enzymes was 3 0,500. The homogeneous proteins cross-reacted in western blots with an tiserum against a basic class I potato leaf chitinase.