Solubilization of a particulate UDP-glucose: Sterol β-glucosyl-transferase in developing cotton fibers and seeds and characterization of steryl 6-acyl-d-glucosides

W. Thomas Forsee, University of Texas Health Science Center at San Antonio
Roger A. Laine, University of Texas Health Science Center at San Antonio
Alan D. Elbein, University of Texas Health Science Center at San Antonio


A particulate enzyme fraction from developing cotton fibers catalyzed the transfer of [14C]glucose from UDP-[14C]glucose to endogenous sterol acceptors, and in turn catalyzed the esterification of the steryl glucosides with fatty acids from an endogenous acyl donor. Analysis of the products by gas-liquid chromatography and mass spectrometry revealed that β-sitosterol was the predominant sterol moiety, while campesterol, cholesterol, and stigmasterol were present in smaller amounts. Glucose was the only sugar present, and it appeared to have the β-configuration. Palmitate and oleate were the major acyl components of the esterified steryl glucoside, and these fatty acid moieties appeared to be linked to the 6-position of glucose as indicated by both periodate cleavage and permethylation studies of the esterified steryl glucoside. When the UDP-glucose: sterol glucosyl transferase was solubilized with Triton X-100 and partially purified, it demonstrated an absolute requirement for added sterol acceptor and could utilize both cholesterol and stigmasterol almost as efficiently as β-sitosterol. However, it was specific for UDP-glucose and showed only slight activity with ADP-glucose, GDP-glucose, CDP-glucose, TDP-glucose, UDP-galactose, and UDP-mannose. The reaction rate was stimulated three-fold by the addition of plant lecithins, while egg lecithin had no effect. Intracellular localization studies demonstrated that the membrane vesicles containing the UDP-glucose:sterol glucosyl transferase had a sucrose density gradient profile which was similar to that of several other enzymes thought to be involved in the synthesis of cell wall polysaccharides. © 1974.