Protective role of red blood cells PAF-acetylhydrolase against oxidative siess

有三种亚型被鉴定为PAF-乙酰水解酶(PAF-AH)，它能降解PAF，是炎症和过敏的介质。I型PAF-AH形成由催化亚基组成的低聚体，称为α_1或α_2。在人体血液中，70%的酶活性存在于血浆中，30%的酶活性存在于红细胞中。中性粒细胞、血小板等白细胞总酶活性低于1%。尽管酶的活性很高，但该酶的亚型和生理作用尚不清楚。在本研究中，从容易获得的猪血中进行了酶的纯化。结果表明，猪红细胞中含有α_1/α_2异二聚体和α_2/α_2同源二聚体。虽然AI亚基在胎脑中高表达，但在成人中除精原细胞外，其表达水平很低。而多形核白细胞、血小板等白细胞仅含有α_2/α_2同源二聚体。这一事实表明，该亚基在调节红细胞功能方面起着重要作用。此外，利用针对这些亚基的抗体进行的Western blotting分析表明，人红细胞含有α_1/α_2异二聚体和α_2/α_2同源二聚体，以及人红细胞。由于红细胞不产生PAF，并且缺乏PAF受体，对该酶的生理底物不被认为是PAR，因此我们将重组PAF-AH添加到从红细胞膜提取的脂质中，并用质谱仪分析其脂质成分。结果表明，重组PAF-AH能降解以Cu2+为底物的红细胞膜的氧化修饰脂类。

Three kinds of subtypes have been identified as PAF-acetylhydrolase (PAF-AH) which degrades PAF ; mediator of inflammation and allergy. Those consist of plasma-type, distributed in body fluids such as plasma, and intracellular type I and type II. Type I PAF-AH forms oligomer consisting of catalytic subunits termed α_1 or α_2. In the human blood, 70 % of enzyme activity is detected in plasma, while 30 % of enzyme activity is detected in red blood cells. Total enzyme activity of white blood cells such as polymorphonuclear leukocytes and platelets was less than 1 %. Despite high occupancy of enzyme activity, subtype of this enzyme and physiological role remain unknown. In this study, enzyme purification was undertaken from easily available pig blood. As a result, it was clarified that pig red blood cells contained α_1/ α_2 heterodimer and α2/α2 homodimer. Although ai subunit is highly expressed in fetal brain, expression of this subunit is very low in the adult except spermatogonium. By contrast, white blood cells such as polymorphonuclear leukocytes and platelets contained α_2/α_2 homodimer alone. This fact suggests that this subunit plays an important role in regulation of red blood cells function. In addition, Western blotting analysis using specific antibodies to these subunits showed that human red blood cells contained α_1/α_2 heterodimer and α_2/α_2 homodimer, as well as human red blood cells.Since red blood cells do not produce PAF and lack PAF receptor, physiological substrate towards this enzyme is not thought to be PAR Thus, we added recombinant PAF-AH to the lipids extracted from red blood cells membranes and analyzed the lipid constituents by mass-spectrometry. As a result, it was shown that recombinant PAF-AH degraded oxidatively modified lipids of the red blood cells membranes exposed by Cu^<2+> as the substrates.