Soubeyrand S, Thérien I, Manjunath P
Department of Medicine, University of Montreal, Montreal, Que., Canada.
Biochim Biophys Acta. 1998 Jun 15;1392(2-3):176-84. doi: 10.1016/s0005-2760(98)00037-x.
The enzyme responsible for most of the phospholipase A2 (PLA2) activity present in bovine seminal plasma was recently purified to homogeneity. Sequencing revealed that the enzyme is also a platelet-activating factor acetylhydrolase (PAF-AH) of the serum type with kinetic properties generally similar to its serum homologue. In the present work, we have attempted to clarify its physiological function by studying its association properties in seminal plasma. As was observed previously for its PLA2 activity, its PAF-AH activity was also inhibited by the major proteins of bovine seminal plasma (BSP proteins). Sequential dilution experiments as well as centrifuging semen on Percoll did not reveal detectable association of PAF-AH with spermatozoa. Neither did the enzyme interact with lipid particles reported to be present in bovine seminal plasma. The purified PAF-AH, however, did display lipoprotein association properties in vitro similar to those demonstrated by the serum enzyme in vivo. At pH 7.4, it could associate with both low density lipoproteins and very low density lipoproteins but not with high density lipoproteins. Overall the data presented here indicate that the enzyme is strongly inactivated as a PAF-AH in seminal plasma and that it does not associate with lipid particles or spermatozoa.
最近，牛精浆中大部分磷脂酶A2（PLA2）活性所对应的酶被纯化至同质状态。测序显示，该酶也是血清型血小板活化因子乙酰水解酶（PAF-AH），其动力学特性与其血清同源物总体相似。在本研究中，我们试图通过研究其在精浆中的缔合特性来阐明其生理功能。正如之前观察到的其PLA2活性一样，其PAF-AH活性也受到牛精浆主要蛋白质（BSP蛋白）的抑制。连续稀释实验以及在Percoll上对精液进行离心，均未发现PAF-AH与精子有可检测到的缔合。该酶也未与据报道存在于牛精浆中的脂质颗粒相互作用。然而，纯化的PAF-AH在体外确实表现出与血清酶在体内所表现出的相似的脂蛋白缔合特性。在pH 7.4时，它可与低密度脂蛋白和极低密度脂蛋白缔合，但不与高密度脂蛋白缔合。总体而言，此处呈现的数据表明该酶在精浆中作为PAF-AH被强烈灭活，且它不与脂质颗粒或精子缔合。
