Enzymic mechanism of starch synthesis in sweet potato roots: II. Enhancement of the starch synthetase activity by maltooligosaccharides

Abstract

The effect of maltooligosaccharides on the transglucosylation reaction catalyzed by the granules-bound starch synthetase of sweet potato roots was studied. The stimulatory effect of oligosaccharides on the incorporation of 14C-glucose into starch granules (starch synthesis) was found to be novel, and not due to the mere adherence of the radioactive oligosaccharides formed by the transglucosylation reaction (oligosaccharide synthesis). The stimulatory effect of K + and oligosaccharide on the enzyme reaction proved to be additive, if ADPG was used as the glucose donor. However, there exists an optimal level of K + for the enzymic transglucosylation reaction, if UDPG was used as the glucose donor. At high levels of K +, oligosaccharide did not exhibit any stimulatory effect. Over the entire range of added K +, the rate of oligosaccharide synthesis appeared to exceed that of the starch-synthesizing reaction. The addition of glucose was found to suppress the starch-synthesizing reaction using both ADPG and UDPG as the glucose donors. The mutual interaction of glucose with K + and with maltooligosaccharide in the starch synthesizing reaction was studied.