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Steryl Glycoside Formation in Seedlings of Nicotiana tabacum L. ¹

^a Department of Agronomy, University of Kentucky, Lexington, Kentucky 40506

Particulate enzyme preparations from tobacco seedlings (Nicotiana tabacum L.) were used in the synthesis of steryl glycoside. The data obtained by measuring cholesterol-4-¹⁴C incorporation generally agree with results obtained with UDP-glucose-¹⁴C. The in vitro reaction was linear for the first 10 minutes and had a pH optimum of 7.0 to 7.4. Addition of ATP activated while UDP-glucose inhibited slightly the reaction. In short term experiments, the percentage disappearance of endogenous and added sterol was about the same.

Intact tobacco seedlings incorporated cholesterol-4-¹⁴C and sitosterol-4-¹⁴C into their steryl glycosides. The acylated steryl glycosides were more rapidly labeled than the nonacylated form. After 12 hours of incubation with cholesterol-4-¹⁴C, about 5% of the radioactivity was recovered as steryl glycoside and 12% as acylated steryl glycoside. Incubation for 12 hours with authentic cholesteryl-¹⁴C glucoside gave only a 4% acylation, and under these conditions 21% of the radioactivity was recovered as free cholesterol. It is suggested that acylated steryl glycosides may be formed through the acylation of steryl glycosides or the transfer of an acyl-glycosyl group to sterol.

¹ Part of Ph.D. thesis of Parshall B. Bush and supported in part by University of Kentucky Research Foundation Grant 7000166. This paper (No. 73-3-55) is part of a project of the Kentucky Agricultural Experiment Station and is published with approval of the Director.