Membrane-bound UDP-Glucose

An enzymic preparation from peas (Pisum satisum), able to form neutral and polar glycosides, is described. The best sugar donor is UDP-glucose and the acceptors are present in the enzymic system.The neutral glycolipids have been characterized as steryl and acylated steryl glucosides. The polar glucolipid had been identified as polyprenyl monophosphate glucose. The glucose is linked to the phosphate in beta configuration. Polar glucolipids are also formed from UDP-glucose and exogenous prenylic acceptors, either alpha-saturated, as dolichyl monophosphate, or allylic, as ficaprenyl monophosphate.THE TWO GLUCOSYLATING ACTIVITIES HAVE BEEN PARTIALLY SEPARATED BY DIFFERENTIAL CENTRIFUGATION: the fraction that precipitates at 25,000g has most of the neutral glucolipid-synthesizing activity, and the fraction that sediments at 100,000g is rich in polar glucolipid glucosyl transferase activity. This latter activity was strongly dependent on Mg(2+) concentration, the optimum being around 5 to 10 mm. UDP inhibits the reaction and 0.2 to 0.5% (v/v) Triton X-100 has a stimulatory effect. The optimum pH is 7.5.