Phospholipase A2 activity of low density lipoprotein: evidence for an intrinsic phospholipase A2 activity of apoprotein B-100.

During oxidative modification of low density lipoprotein (LDL) there is extensive degradation of phosphatidylcholine (PtdCho) to lysophosphatidylcholine (lyso-PtdCho), with the removal of fatty acids from the 2 position. The phospholipase A2 (PLA2) activity responsible for hydrolysis is closely associated with LDL. By use of lipoxygenase-oxidized 2-[1-14C]linoleoyl PtdCho as the substrate and delipidated apoprotein B (apo-B), evidence is presented to show that (i) the activity is destroyed progressively during the oxidative modification of LDL; (ii) p-bromophenacyl bromide (pBPB), a histidine modifier that inhibits the oxidative modification of LDL, also substantially inhibits the PLA2 activity; and (iii) photooxidation of LDL in the presence of Rose Bengal completely inactivates the enzyme with concomitant loss of apo-B histidine residues. High molecular weight proteins from delipidated LDL, separated by polyacrylamide gel electrophoresis, showed PLA2 activity. It is suggested that apo-B itself may possess PLA2 activity.

在低密度脂蛋白（low density lipoprotein, LDL）的氧化修饰过程中，磷脂酰胆碱（phosphatidylcholine, PtdCho）会被广泛降解为溶血磷脂酰胆碱（lysophosphatidylcholine, lyso-PtdCho），其2号位的脂肪酸被移除。负责该水解反应的磷脂酶A2（phospholipase A2, PLA2）活性与LDL紧密关联。本研究以脂氧合酶氧化的2-[1-14C]亚油酰基磷脂酰胆碱作为底物，并使用去脂载脂蛋白B（delipidated apoprotein B, apo-B），提供了如下证据：(i) 该酶活会在LDL氧化修饰过程中逐渐丧失；(ii) 对溴苯甲酰溴（p-bromophenacyl bromide, pBPB）——一种可抑制LDL氧化修饰的组氨酸修饰剂——同样可显著抑制PLA2活性；(iii) 在孟加拉玫瑰红（Rose Bengal）存在下对LDL进行光氧化处理，可完全灭活该酶，同时伴随apo-B组氨酸残基的丢失。经聚丙烯酰胺凝胶电泳（polyacrylamide gel electrophoresis）分离得到的去脂LDL高分子量蛋白组分，显示出PLA2活性。研究提示apo-B本身可能具备PLA2活性。