Shibata Y, Abiko Y, Ohno H, Araki T, Takiguchi H
Department of Biochemistry, Nihon University School of Dentistry, Matsudo, Japan.
Life Sci. 1988;43(11):889-96. doi: 10.1016/0024-3205(88)90264-0.
Phospholipase (PLase) activities in the plasma membrane of guinea pig peritoneal macrophages were studied, as these enzymes having such activity may be candidates for the release of arachidonic acid (AA) from phosphatidylcholine (PC). An AA release system operating at acidic pH was identified in the macrophage plasma membrane and characterized. This membrane-bound acidic PLase A2 had an optimum pH at 4.5, and enzyme activation was observed in Ca++-free medium; but the maximum activity was found at 0.5 mM Ca++ concentration. The Km value for PC of acidic PLase A2 was 4.2 microM, and a Michaelis-Menten relationship was evident. Calcium might act as a cofactor at some intermediate step during the activation of acidic PLase A2 in light of the uncompetitive manner of Ca++ action. Furthermore, the release of [3H]-AA from preradiolabelled macrophage plasma membranes occurred with the addition of Ca++ at pH 4.5. These data suggest that the acid PLase A2 is a component of the plasma membrane and is not due to lysosomal contamination since membrane-bound acidic PLase A2 properties are opposite to those found for lysosomal PLase A2.
对豚鼠腹膜巨噬细胞质膜中的磷脂酶（PLase）活性进行了研究，因为具有这种活性的这些酶可能是从磷脂酰胆碱（PC）释放花生四烯酸（AA）的候选酶。在巨噬细胞质膜中鉴定并表征了一种在酸性pH下运行的AA释放系统。这种膜结合的酸性磷脂酶A2的最适pH为4.5，在无Ca++的培养基中观察到酶激活；但在Ca++浓度为0.5 mM时发现最大活性。酸性磷脂酶A2对PC的Km值为4.2 microM，呈现明显的米氏关系。鉴于Ca++作用的非竞争性方式，钙可能在酸性磷脂酶A2激活的某些中间步骤中作为辅助因子。此外，在pH 4.5时添加Ca++会导致预放射性标记的巨噬细胞质膜释放[3H]-AA。这些数据表明酸性磷脂酶A2是质膜的一个组成部分，并非由于溶酶体污染，因为膜结合的酸性磷脂酶A2的特性与溶酶体磷脂酶A2的特性相反。
