Studies on the Biosynthesis of Starch: II. SOME PROPERTIES OF THE ADENOSINE DIPHOSPHATE GLUCOSE:STARCH GLUCOSYLTRANSFERASE BOUND TO THE STARCH GRANULE

Abstract

The properties of the particulate starch synthetase from different sources were studied. The specificity of this enzyme toward a number of sugar nucleotides and its Km values and maximum velocities were determined. The properties of the particulate enzyme were considerably changed when the structure of the granules was modified by mechanical disruption. After this treatment uridine diphosphate glucose was no longer a substrate, while the activity with adenosine diphosphate glucose was enhanced. The new specificity is similar to that of the soluble glucan synthetases. The results obtained would suggest that both the synthetase bound to the granule and the soluble synthetase could be different forms of the same enzyme. The addition of branching enzyme considerably increased the incorporation of glucosyl moieties into the intact grain or into the amylopectin left after the granule was ground. The action of α- and β-amylase and of concentrated urea solutions on the starch grains was also studied.