Higgs H N, Glomset J A
Department of Biochemistry, Howard Hughes Medical Institute, University of Washington, Seattle 98195.
Proc Natl Acad Sci U S A. 1994 Sep 27;91(20):9574-8. doi: 10.1073/pnas.91.20.9574.
Recent experiments in several laboratories have provided evidence that phosphatidic acid functions in cell signaling. However, the mechanisms that regulate cellular phosphatidic acid levels remain obscure. Here we describe a soluble phospholipase A1 from bovine testis that preferentially hydrolyzes phosphatidic acid when assayed in Triton X-100 micelles. Moreover, the enzyme hydrolyzes phosphatidic acid molecular species containing two unsaturated fatty acids in preference to those containing a combination of saturated and unsaturated fatty acyl groups. Under certain conditions, the enzyme also displays lysophospholipase activity toward lysophosphatidic acid. The phospholipase A1 is not likely to be a lysosomal enzyme because its optimum pH is 7.5-8.5. Furthermore, it is probably not a general lipid metabolic enzyme because high levels of activity are found in mature testis and brain but no measurable activity is seen in liver, spleen, or heart. The fact that the activity of the phospholipase A1 in mature bovine testis is > 10-fold higher than that in newborn calf testis raises the possibility that the enzyme may play a regulatory role in spermatogenesis or sperm function.
最近在几个实验室进行的实验提供了证据，表明磷脂酸在细胞信号传导中发挥作用。然而，调节细胞内磷脂酸水平的机制仍不清楚。在这里，我们描述了一种来自牛睾丸的可溶性磷脂酶A1，当在Triton X-100微团中进行测定时，它优先水解磷脂酸。此外，该酶优先水解含有两个不饱和脂肪酸的磷脂酸分子种类，而不是含有饱和与不饱和脂肪酰基组合的那些种类。在某些条件下，该酶对溶血磷脂酸也表现出溶血磷脂酶活性。这种磷脂酶A1不太可能是溶酶体酶，因为其最适pH为7.5 - 8.5。此外，它可能不是一种普遍的脂质代谢酶，因为在成熟睾丸和大脑中发现了高水平的活性，但在肝脏、脾脏或心脏中未检测到可测量的活性。成熟牛睾丸中磷脂酶A1的活性比新生小牛睾丸中的活性高10倍以上，这一事实增加了该酶可能在精子发生或精子功能中发挥调节作用的可能性。
