IDENTIFICATION OF A PHOSPHATIDIC ACID-PREFERRING PHOSPHOLIPASE A(1) FROM BOVINE BRAIN AND TESTIS

Recent experiments in several laboratories have provided evidence that phosphatidic acid functions in cell signaling. However, the mechanism s that regulate cellular phosphatidic acid levels remain obscure. Here we describe a soluble phospholipase A(1) from bovine testis that pref erentially hydrolyzes phosphatidic acid when assayed in Triton X-100 m icelles. Moreover, the enzyme hydrolyzes phosphatidic acid molecular s pecies containing two unsaturated fatty acids in preference to those c ontaining a combination of saturated and unsaturated fatty acyl groups . Under certain conditions, the enzyme also displays lysophospholipase activity toward lysophosphatidic acid. The phospholipase A(1) is not likely to be a lysosomal enzyme because its optimum pH is 7.5-8.5. Fur thermore, it is probably not a general lipid metabolic enzyme because high levels of activity are found in mature testis and brain but no me asurable activity is seen in liver, spleen, or heart. The fact that th e activity of the phospholipase A(1) in mature bovine testis is >10-fo ld higher than that in newborn calf testis raises the possibility that the enzyme may play a regulatory role in spermatogenesis or sperm fun ction.