Soluble adenosine diphosphate glucose- -1,4-glucan -4-glucosyltransferases from spinach leaves

Abstract

Multiple forms of ADP-glucose-alpha-1,4-glucan alpha-4-glucosyltransferase were obtained from spinach leaves by gradient elution from a DEAE-cellulose column. In the presence of high concentrations of some salts and bovine serum albumin, unprimed activity was found in one (transglucosylase III) of the four fractions eluted from the column. In addition to having unprimed activity, transglucosylase III had a lower K(m) for ADP-glucose, a much higher K(m) for oyster glycogen, greater heat sensitivity and lower affinity for maltose, maltotriose and amylopectin beta-limit dextrin than fractions I, II and IV. In addition, the kinetics at low concentrations of amylose, amylopectin and rabbit liver glycogen were non-linear for transglucosylase III. The properties of transglucosylases I, II and IV were generally similar to each other. Rates of the unprimed reaction at physiological concentrations of ADP-glucose were greater than those found for the primed reaction of fraction III. The product formed by the unprimed reaction was a glucan containing principally alpha-1,4 linkages with some alpha-1,6 linkages. The primer, maltose, at a concentration of 0.5m inhibited the synthesis of the unprimed product.