Abstract
A previously detected phosphatidylcholine-specific phospholipase D from lysates of human red blood cells has been further characterized by 1H spin-echo n.m.r. spectroscopy. A second choline-releasing enzymic activity was observed after addition of glycerophosphocholine. Both of these phosphoric diester hydrolase activities were activated to different extents by different concentrations of calcium ions. Differences between the two activities were also observed on inhibition by barium and phosphate ions. These distinct, choline-yielding, reactions which occur in the cytoplasm of red blood cells may be involved in the regulation of the levels of membrane phosphatidylcholine.