Abstract
Phosphatidylcholine phosphatidohydrolase (EC 3.1.4.4, phospholipase D) catalyzes the hydrolysis of phosphatidylcholine to phosphatidic acid and choline. We have developed a spectrophotometric assay for phospholipase D using choline kinase, pyruvate kinase, and lactate dehydrogenase to couple the release of choline with the oxidation of NADH. The assay was linear both with time and with enzyme concentration. The assay should prove useful for continuous monitoring of enzyme activity, determination of initial rates of reaction, and detailed kinetic studies of phospholipase D. The method is limited to analysis of purified preparations of phospholipase D lacking competing activities to the coupled system.