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 mechanisms that regulate cellular phosphatidic acid levels remain obscure. Here we describe a soluble phospholipase A(1) 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 A(1) 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 A(1) 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.