Steryl glycoside formation in seedlings of Nicotiana tabacum L

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.