Tokumura A, Nishioka Y, Yoshimoto O, Shinomiya J, Fukuzawa K
Faculty of Pharmaceutical Sciences, The University of Tokushima, Tokushima, 1-78, Shomachi 770-8505, Japan.
Biochim Biophys Acta. 1999 Feb 25;1437(2):235-45. doi: 10.1016/s1388-1981(99)00011-6.
Previously we reported that lysophospholipase D in rat plasma hydrolyzes endogenous unsaturated lysophosphatidylcholines (LPCs) preferentially to saturated LPCs to lysophosphatidic acids with growth factor-like and hormone-like activities. In this study, we examined the possibility that association of LPCs with different proteins in rat plasma has an effect on the preference of lysophospholipase D for unsaturated LPCs. Large portions of various LPCs were found to be recovered in the lipoprotein-poor bottom fraction. Furthermore, the percentages of LPCs associated with albumin isolated from rat plasma were shown not to be consistent with their percentage conversions to lysophosphatidic acids by lysophospholipase D on incubation of rat plasma at 37 degrees C. These results indicate that distinct distributions of LPCs in the plasma protein fractions are not critical factors for the substrate specificity of lysophospholipase D. Experiments with Nagase analbuminemic rats suggested that albumin-LPC complexes are not necessarily required for the hydrolysis by lysophospholipase D; lipoprotein-associate LPCs appeared to be good substrates for the phospholipase. We found that both saturated and unsaturated LPCs are present mainly as 1-acyl isomers in rat plasma. This result indicates that the preference of lysophospholipase D for unsaturated LPCs is not attributable to a difference in position of the acyl group attached to the glycerol backbone of LPC. In addition, lysophospholipase D was also found to attack choline phospholipids with a long chain group and a short chain alkyl group, although their percentage hydrolyses were low. Taken altogether, these results suggest that lysophospholipase D shows higher affinities for free forms of unsaturated acyl type LPCs equilibrated with albumin-bound and lipoprotein-associated forms, than for free forms of saturated acyl type LPCs and analogs of platelet-activating factor.
此前我们报道，大鼠血浆中的溶血磷脂酶D优先水解内源性不饱和溶血磷脂酰胆碱（LPC）而非饱和LPC，生成具有生长因子样和激素样活性的溶血磷脂酸。在本研究中，我们探讨了大鼠血浆中LPC与不同蛋白质的结合是否会影响溶血磷脂酶D对不饱和LPC的偏好性。发现各种LPC的大部分存在于脂蛋白含量低的底部组分中。此外，从大鼠血浆中分离出的与白蛋白结合的LPC百分比，与在37℃孵育大鼠血浆时它们被溶血磷脂酶D转化为溶血磷脂酸的百分比并不一致。这些结果表明，LPC在血浆蛋白组分中的不同分布并非溶血磷脂酶D底物特异性的关键因素。对长谷无白蛋白血症大鼠的实验表明，溶血磷脂酶D水解不一定需要白蛋白-LPC复合物；与脂蛋白结合的LPC似乎是该磷脂酶的良好底物。我们发现，饱和和不饱和LPC在大鼠血浆中主要以1-酰基异构体形式存在。这一结果表明，溶血磷脂酶D对不饱和LPC的偏好并非归因于LPC甘油主链上连接的酰基位置差异。此外，还发现溶血磷脂酶D也能作用于具有长链基团和短链烷基的胆碱磷脂，尽管它们的水解百分比很低。综上所述，这些结果表明，与白蛋白结合和脂蛋白相关形式平衡的不饱和酰基型LPC游离形式相比，溶血磷脂酶D对饱和酰基型LPC游离形式和血小板活化因子类似物具有更高的亲和力。
