Department of Periodontology and Section of Physiological Chemistry, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-Ku, Tokyo, 113, Japan.
Platelets. 1992;3(1):23-7. doi: 10.3109/09537109209013164.
It is known that both platelet-activating factor (PAF) acetylhydrolase and phospholipase A(2) can inactivate PAF. An enzyme with the ability to convert labelled PAF into lyso-PAF was detected in the culture medium of mouse calvaria cultured in serum-free BG Jb medium containing 0.1% bovine serum albumin. The enzyme was unable to degrade labelled long chain diacylphosphatidylcholine, and was inert to addition of Ca(2+) (10 mM) or EDTA (10 mM). The enzyme was inhibited by diisopropylfluorophosphate in a dose-dependent manner. Moreover, the enzyme was found to be acid-labile, in a similar manner to PAF acetylhydrolase in mouse plasma. Based on these data, the enzyme was identified as PAF acetylhydrolase. It is known that PAF acetylhydrolase in rat plasma is different from that in rat kidney cortex in its sensitivity to proteases. PAF acetylhydrolase in mouse calvaria was insensitive to trypsin and pronase, like PAF acetylhydrolase in mouse plasma, while PAF acetylhydrolase in mouse kidney cortex was sensitive. PAF acetylhydrolase activity in the culture medium increased time-dependently for at least 48 h. Treatment of calvaria for 12 h with cycloheximide (1 μg/ml), an inhibitor of protein synthesis, almost completely prevented the appearance of acetylhydrolase activity in the culture medium. Thus, the results suggest that mouse calvaria synthesize PAF acetylhydrolase and release it extracellularly under no stimuli, and that the properties of the acetylhydrolase in calvaria are similar to those of the enzyme found in plasma. Therefore, mouse calvaria may be one of the origins of PAF acetylhydrolase in plasma.
已知血小板激活因子（PAF）乙酰水解酶和磷脂酶 A2 都可以使 PAF 失活。在含 0.1%牛血清白蛋白的无血清 BGJb 培养基中培养的鼠颅骨培养物的培养基中，检测到一种能够将标记的 PAF 转化为溶酶体-PAF 的酶。该酶不能降解标记的长链二酰基磷酸磷脂，并且对添加 Ca2+（10mM）或 EDTA（10mM）没有反应。该酶被二异丙基氟磷酸以剂量依赖的方式抑制。此外，该酶表现出酸不稳定，与鼠血浆中的 PAF 乙酰水解酶相似。基于这些数据，该酶被鉴定为 PAF 乙酰水解酶。已知大鼠血浆中的 PAF 乙酰水解酶与其在大鼠肾皮质中的敏感性不同，对蛋白酶敏感。鼠颅骨中的 PAF 乙酰水解酶对胰蛋白酶和蛋白酶无反应，与鼠血浆中的 PAF 乙酰水解酶相似，而鼠肾皮质中的 PAF 乙酰水解酶敏感。培养物中 PAF 乙酰水解酶活性至少在 48 小时内随时间呈时间依赖性增加。用蛋白合成抑制剂环己亚胺（1μg/ml）处理颅骨 12 小时，几乎完全阻止了培养物中乙酰水解酶活性的出现。因此，结果表明，鼠颅骨在无刺激的情况下合成 PAF 乙酰水解酶并将其释放到细胞外，并且颅骨中乙酰水解酶的特性与在血浆中发现的酶相似。因此，鼠颅骨可能是血浆中 PAF 乙酰水解酶的来源之一。
