Solubilization of the UDP-glucose:1,4-beta-D-glucan 4-beta-D-glucosyltransferase (cellulose synthase) from Acetobacter xylinum. A comparison of regulatory properties with those of the membrane-bound form of the enzyme

Abstract

A procedure has been developed for the effective solubilization of UDP-glucose:1,4-beta-D-glucan 4-beta-D-glucosyltransferase (cellulose synthase) by treatment of membranes from the bacterium Acetobacter xylinum with digitonin. Low concentrations of digitonin (0.1%, w/v) cause stimulation of the enzyme activity in membranes; treatment with higher concentrations of digitonin (1-10%) results in solubilization of up to 70% of the digitonin-stimulated activity. The digitonin-solubilized enzyme displays regulatory properties quite similar to those of the membrane-bound form of the enzyme, showing specific activation by GTP. GTP activation requires the presence of a protein factor which can be separated from the enzyme by washing the membranes prior to enzyme solubilization. Association of this protein factor with the membrane-bound enzyme is promoted by polyethylene glycol or by Ca2+; however, these compounds are ineffective in enhancing enzyme-factor association for the enzyme in the solubilized state. The observation that Ca2+ promotes enzyme-factor association in the membranes suggests that this cation, in addition to GTP, may play a role in the regulation of cellulose synthesis in vivo in A. xylinum.