Schnitzer E, Pinchuk I, Fainaru M, Lichtenberg D, Yedgar S
Department of Physiology, Tel-Aviv University, Sackler Faculty of Medicine, Israel.
Free Radic Biol Med. 1998 May;24(7-8):1294-303. doi: 10.1016/s0891-5849(97)00454-1.
The irreversible proteinase inhibitor Pefabloc (4-[2-aminoethyl] benzenesulfonyl fluoride) inactivates LDL-catalyzed hydrolysis of the short-chain fluorescent phospholipid C6-NBD-PC (1-acyl-2-(N-4-nitrobenzo-2-oxa-1,3-diazole)-aminocaproyl phosphatidylcholine). The dose-dependence of this inactivation is similar to that obtained previously for the inhibitory effect of Pefabloc on the hydrolysis of platelet activating factor (PAF) by the LDL-associated PAF acetylhydrolase (PAF-AH), in agreement with the notion that the hydrolysis of C6-NBD-PC and PAF is catalyzed by the same enzyme (LDL-associated phospholipase A; LDL-PLA). This conclusion is also supported by the finding that hydrolysis of C6-NBD-PC by LDL becomes inactivated by LDL oxidation only at late stages of the oxidation, similar to the effect of oxidation on the hydrolysis of PAF by the LDL-associated PAF-AH. Under conditions of complete inactivation of this enzyme towards C6-NBD-PC, the kinetics of lipid peroxidation, induced either by copper ions or by the free radical generator AAPH at varying doses of the prooxidant, was similar to that observed when the PLA was active (i.e., in the absence of Pefabloc). Hence, LDL-associated PLA (PAF-AH) does not protect LDL lipids from peroxidation. Similar results were obtained with fractionated LDL in albumin-containing buffer and for non-fractionated serum, in which copper-induced peroxidation was also not influenced by inactivation of the enzyme responsible for hydrolysis of C6-NBD-PC. Phospholipolysis of short chain phospholipids by LDL-PLA may still play a protective role against the toxic effects of oxidized phospholipids by reducing their internalization into cells (Schmitt et al. 1995).
不可逆蛋白酶抑制剂苯甲磺酰氟（4-[2-氨基乙基]苯磺酰氟）可使低密度脂蛋白（LDL）催化的短链荧光磷脂C6-NBD-PC（1-酰基-2-（N-4-硝基苯并-2-恶唑-1,3-二唑）-氨基己酰磷脂酰胆碱）水解失活。这种失活的剂量依赖性与之前观察到的苯甲磺酰氟对LDL相关的血小板活化因子（PAF）乙酰水解酶（PAF-AH）催化的PAF水解的抑制作用相似，这与C6-NBD-PC和PAF的水解由同一种酶（LDL相关磷脂酶A；LDL-PLA）催化的观点一致。这一结论还得到以下发现的支持：LDL对C6-NBD-PC的水解仅在氧化后期因LDL氧化而失活，类似于氧化对LDL相关PAF-AH催化的PAF水解的影响。在该酶对C6-NBD-PC完全失活的条件下，由铜离子或不同剂量的自由基引发剂AAPH诱导的脂质过氧化动力学与PLA有活性时（即不存在苯甲磺酰氟时）观察到的相似。因此，LDL相关的PLA（PAF-AH）不能保护LDL脂质免于过氧化。在含白蛋白缓冲液中的分级LDL以及未分级血清中也得到了类似结果，其中铜诱导的过氧化也不受负责C6-NBD-PC水解的酶失活的影响。LDL-PLA对短链磷脂的磷脂分解可能仍通过减少氧化磷脂内化进入细胞而对其毒性作用起到保护作用（施密特等人，1995年）。
