Abstract
Adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] was solubilized from a rat brain homogenate with sodium deoxycholate. This solubilized preparation had no detectable enzymic activity with either Mg-ATP or Mn-ATP as substrate. The activity could be restored by addition of either nonionic detergent or certain specific phospholipids. Maximal restoration of enzyme activity was obtained with Triton X-100, L-alpha-phosphatidylcholine, L-alpha-lysophosphatidylcholine, phosphatidyl-N-monomethylethanolamine, or sphingomyelin. Activity was only partially restored by phosphatidylethanolamine (40-60%) or phosphatidyl-N,N-dimethylethanolamine (10-20%). Other phospholipids tested, including phosphatidylserine, phosphatidylglycerol, phosphatidylinositol, and phosphatidic acid, could not restore enzyme activity but, instead, could inhibit the stimulation of enzyme activity by phosphatidylcholine. The restoration of activity by L-alpha-phosphatidylcholine was inhibited by cholesterol at concentrations above 33 mol %, although this effect was not observed with three different esters of cholesterol. These studies suggest a possible specific role of phospholipids in modulating adenylate cyclase activity.