Rotenberg M, Zakim D
Department of Medicine, Cornell University Medical College, New York, New York 10021.
J Biol Chem. 1991 Mar 5;266(7):4159-61.
The effects of cholesterol on the activity and thermal properties of a pure, delipidated isoform of UDP-glucuronosyltransferase were examined after incorporation of enzyme into unilamellar bilayers of distearoylphosphatidylcholine (DSPC) or dioleoylphosphatidylcholine (DOPC). Cholesterol, in bilayers of DSPC, decreased enzyme activity and lowered the temperature (from 37 to 30 degrees C) for a reversible transition from the active form of the enzyme to a less active form. These effects could be separated from each other in that the effect on reversible inactivation of the enzyme occurred at lower concentrations of cholesterol than the effect on activity of the active form of the enzyme. In addition, cholesterol in bilayers of DSPC stabilized UDP-glucuronosyltransferase against irreversible thermal inactivation. The extent of stabilization increased with increasing concentration of cholesterol in the bilayers. The effects of cholesterol on UDP-glucuronosyltransferase depended, however, on the nature of the bilayer containing cholesterol. Cholesterol had small effects, if any, on the properties of UDP-glucuronosyltransferase in bilayers of DOPC.
将UDP - 葡萄糖醛酸基转移酶的纯脱脂蛋白形式掺入二硬脂酰磷脂酰胆碱（DSPC）或二油酰磷脂酰胆碱（DOPC）的单层双分子层后，研究了胆固醇对其活性和热性质的影响。在DSPC双分子层中，胆固醇降低了酶活性，并降低了酶从活性形式可逆转变为活性较低形式的温度（从37℃降至30℃）。这些效应可以相互分离，因为对酶可逆失活的影响发生在比影响酶活性形式的活性更低的胆固醇浓度下。此外，DSPC双分子层中的胆固醇使UDP - 葡萄糖醛酸基转移酶对不可逆热失活具有稳定性。稳定程度随着双分子层中胆固醇浓度的增加而增加。然而，胆固醇对UDP - 葡萄糖醛酸基转移酶的影响取决于含有胆固醇的双分子层的性质。胆固醇对DOPC双分子层中UDP - 葡萄糖醛酸基转移酶的性质影响很小（如果有影响的话）。
