Serres-Guillaumond M, Louisot P
Biochim Biophys Acta. 1983 Apr 13;751(2):247-53. doi: 10.1016/0005-2760(83)90179-0.
A galactosyltransferase activity is located in the cell-sap of aortic intima-media cells. This enzymatic system calatyzes [14C]galactose transfer from UDP-[14C]galactose into endogenous and exogenous proteinic acceptors. Labelled products are isolated from the proteinic fraction obtained in 20% trichloroacetic acid pellet or from organic solvent extractions. Maximal [14C]galactose incorporation occurs at pH 7.8 in Tris-HCl buffer in the presence of 0.1 mM MnCl2 at 30 degrees C. The enzymatic activity is modified by phospholipids, particularly by phosphatidic acid and lysophosphatidylcholine, which behave as mixed inhibitors, while L-alpha-phosphatidylserine interacts as a competitive inhibitor. The effect of phospholipids is not stereospecific but appeared to be closely related to their polar headgroups, especially the acidic headgroups of phosphatidylcholine and phosphatidic acid. The chain length and the unsaturation degree of fatty acids involved in phospholipid structures are not a main factor of regulation. The lysophosphatidylcholine effect could be explained by its solubilization properties, as non-ionic detergents interact in the same way with galactosyltransferase activity. Exogenous phospholipids probably interact with the enzymatic environment by their own molecular arrangement and so could exert a control on galactosyltransferase activity or lead to a conformation change of this enzyme.
半乳糖基转移酶活性存在于主动脉内膜 - 中膜细胞的细胞液中。该酶系统催化[14C]半乳糖从UDP - [14C]半乳糖转移到内源性和外源性蛋白质受体中。标记产物从20%三氯乙酸沉淀中获得的蛋白质部分或有机溶剂提取物中分离出来。在30℃下，于含有0.1 mM MnCl2的Tris - HCl缓冲液中，pH 7.8时[14C]半乳糖掺入量最大。磷脂可修饰该酶活性，特别是磷脂酸和溶血磷脂酰胆碱，它们表现为混合型抑制剂，而L-α-磷脂酰丝氨酸作为竞争性抑制剂起作用。磷脂的作用不是立体特异性的，但似乎与其极性头部基团密切相关，尤其是磷脂酰胆碱和磷脂酸的酸性头部基团。参与磷脂结构的脂肪酸的链长和不饱和度不是调节的主要因素。溶血磷脂酰胆碱的作用可以用其增溶特性来解释，因为非离子洗涤剂与半乳糖基转移酶活性的相互作用方式相同。外源性磷脂可能通过自身的分子排列与酶环境相互作用，从而对半乳糖基转移酶活性进行控制或导致该酶的构象变化。
