Erman A, Azuri R, Raz A
Biochem J. 1982 Mar 1;201(3):635-40. doi: 10.1042/bj2010635.
We have recently shown that mitochondrial and plasma-membrane fractions from kidney medulla possess Ca(2+)-stimulated acylhydrolase and prostaglandin synthase activities. The nature of the enzymic coupling between the Ca(2+)-stimulated arachidonic acid release and its subsequent conversion into prostaglandins was investigated in subcellular fractions from rabbit kidney medulla. Plasma-membrane, mitochondrial and microsomal fractions were found to have similar apparent K(m) values for conversion of added exogenous arachidonate into prostaglandins. The rate of prostaglandin biosynthesis (V(max.)) from added arachidonic acid in the microsomal fraction was approx. 2-fold higher than in the other subcellular fractions. In contrast, prostaglandin E(2) synthesis from endogenous arachidonate in plasma-membrane and mitochondrial fractions was 3-4-fold higher than in microsomes. Furthermore, Ca(2+) stimulated endogenous arachidonate deacylation and prostaglandin E(2) generation in the former two fractions but not in microsomes. In mitochondrial or crude plasma-membrane fractions, in which prostaglandin biosynthesis was inhibited with aspirin, arachidonate released from these fractions was converted into prostaglandins by the microsomal prostaglandin synthase. Thus an intracellular prostaglandin generation process that involves inter-fraction transfer of arachidonic acid can operate. Prostaglandin generation by such an inter-fraction process is, however, less efficient than by an intra-fraction process, where arachidonic acid released by mitochondria or crude plasma membranes is converted into prostaglandins by prostaglandin synthase present in the same fraction. This demonstrates the presence of a tight intra-fraction enzymic coupling between Ca(2+)-stimulated acylhydrolase and prostaglandin synthase enzyme systems in both mitochondrial and plasma-membrane fractions.
我们最近发现，肾髓质的线粒体和质膜部分具有钙刺激的酰基水解酶和前列腺素合酶活性。在兔肾髓质的亚细胞部分中，研究了钙刺激的花生四烯酸释放与其随后转化为前列腺素之间的酶促偶联性质。发现质膜、线粒体和微粒体部分将添加的外源性花生四烯酸转化为前列腺素的表观米氏常数（K(m)）相似。微粒体部分中由添加的花生四烯酸合成前列腺素的速率（V(max.)）约比其他亚细胞部分高2倍。相比之下，质膜和线粒体部分中由内源性花生四烯酸合成前列腺素E2的量比微粒体中高3 - 4倍。此外，钙刺激了前两个部分中内源性花生四烯酸的脱酰作用和前列腺素E2的生成，但在微粒体中未观察到。在前列腺素生物合成被阿司匹林抑制的线粒体或粗质膜部分中，从这些部分释放的花生四烯酸被微粒体前列腺素合酶转化为前列腺素。因此，涉及花生四烯酸在不同部分之间转移的细胞内前列腺素生成过程可以起作用。然而，通过这种不同部分之间的过程生成前列腺素的效率低于通过同一部分内的过程，即线粒体或粗质膜释放的花生四烯酸被同一部分中存在的前列腺素合酶转化为前列腺素。这证明了在线粒体和质膜部分中，钙刺激的酰基水解酶和前列腺素合酶酶系统之间存在紧密的部分内酶促偶联。
