176. Abstract

(1-3)- and (1-4)-B-glucan synthase activities form higher plants have been physically separated by gel electrophoresis in nondenaturing conditions. The two glucan synthases show different mobilities in native polyacrylamide gels. Further separation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a different polypeptide composition in these synthases. Three polypeptides (64, 54, and 32 kD) seem to be common to both synthase activities, whereas two polypeptides ( 78 and 38 kD) are associated only with callose synthase activity. Twelve polypeptides ( 170, 136, 108, 96, 83, 72, 66, 60, 52, 48, 42, and 34 kD) appear to be specifically associated with cellulose synthase activity. The successful separation of (1-3)-and (1-4)-B-glucan synthase activities was based on the manipulation of digitonin concentrations used in the solubilization of membrane proteins. At low digitonin concentrations (0.05 and 0.1%), the ratio of the cellulose to callose synthase activity was higher.  At higher digitonin (0.5-1%) concentrations, the ratio of the callose to cellulose synthase activity was higher. Rosette-like particles with attached product were observed in samples taken from the top of the stacking gel, where only cellulose was synthesized. Smaller (nonrosette) particles were found in the running gel, where only callose was synthesized. These findings suggest that a higher level of subunit organization is required for in vitro cellulose synthesis in comparison with callose assembly.

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