| Abstract: | The Influence of Activators and Inhibitors on Enzymes of the Land's Cycle in Microsomal Membranes The fatty acid exchange of phospholipids in biological membranes is described by the Land's cycle. Acyltransferases and phospholipase A2 are involved in the reacylation and deacylation of phospholipids. The membranes of a microsomal preparation from porcine heart muscle was separated on a Ficoll gradient in plasma membranes (on 10% Ficoll) and membranes of endoplasmic reticulum (on 15% Ficoll). Membranes on 10% Ficoll are designated as fraction F1 and those on 15% Ficoll as fraction F2. Both membrane fractions showed quite different activities for enzymes belonging to the Land's cycle. Enzymes of the Land's cycle of fraction F1 were dependent on magnesium. ATP and CoA. A dependence of ATP but not of CoA could be detected for enzymes in membrane fraction F2. Bromopalmitic acid as inhibitor showed the same results. In a comparable way the inhibitor effect of EDTA was much stronger on membrane fraction F1 than on fraction F2. The stimulation of enzyme activities by calcium effects especially the activities of phospholipase A2 activity are present in both membrane fractions. In addition there might be an activity of acyl-CoA-synthetase in membrane fraction F1 but a comparable activity could not be detected for F2. We suppose that the fatty acid exchange in phospholipids of F2 is not effected by the addition of coenzyme A. Both membrane systems seem to be quite different concerning the enzyme activities representing the Land's cycle. |
