UDP-glucose sterol beta-D-glucosyltransferase, a plasma membrane-bound enzyme of plants: enzymatic properties and lipid dependence.
UDP-glucose sterol beta-D-glucosyltransferase (UDPG-SGTase) catalyzes the glucosylation of plant sterols. This enzyme has been shown to be membrane-bound, most of its activity being associated with plasma membrane in etiolated maize coleoptiles. After solubilization with detergents, total delipidation and purification, kinetic studies performed with a purified enzyme preparation in the presence of detergent and soybean phosphatidylcholine (PC) strongly suggest an ordered bi-bi mechanism for the glucosylation of sterols. A reduced sulfhydryl group and an arginyl residue were shown to be essential for activity. Lipid dependence studies have been performed on the delipidated enzyme in two systems: a micellar one composed of a mixture of enzyme, detergent and phospholipids and another one where the enzymatic activity was reconstituted in unilamellar lipid vesicles. In both systems it was shown that the UDPG-SGTase activity was stimulated to a large extent by negatively charged phospholipids. Enzymatic assays were performed with membrane fractions originating from plants whose sterol content was profoundly modified following treatment with a sterol biosynthesis inhibitor. Results showed that the sterol glucosylating activity was strongly inhibited in these fractions in accordance with sterol substrate specificity studies. All these results show that the UDPG-SGTase is exquisitely sensitive to its lipid environment. Physiological implications of these data are discussed in the light of the putative role of sterols in the plant cell.
Ullmann
P
P
Département d'Enzymologie Cellulaire et Moléculaire, IBMP (UPR 406), Institut de Botanique, Strasbourg, France.
Ury
A
A
Rimmele
D
D
Benveniste
P
P
Bouvier-Navé
P
P
D001665:Binding Sites; D002462:Cell Membrane / Q000201:enzymology; D002846:Chromatography, Affinity; D002852:Chromatography, Ion Exchange; D003902:Detergents; D005964:Glucosyltransferases / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D006031:Glycosylation; D007700:Kinetics; D050356:Lipid Metabolism; D010713:Phosphatidylcholines / Q000378:metabolism*; D010944:Plants / Q000201:enzymology*; D012995:Solubility; D013261:Sterols / Q000378:metabolism; D013379:Substrate Specificity
D003902:Detergents; D010713:Phosphatidylcholines; D013261:Sterols; D005964:Glucosyltransferases; C085360:sterol 3-beta-glucosyltransferase