title: Phospholipid metabolism of stimulated lymphocytes. Comparison of the activation of acyl-CoA:lysolecithin acyltransferase with the binding of concanavalin A to thymocytes.
abstract: Calf thymocytes were isolated and incubated with concanavalin A. The effect of the mitogen on the enzyme activity of membrane-bound lysolecithin acyltransferase (acyl-CoA:1-acylglycero-3-phosphorylcholine-O-acyltransferase, EC 2.3.1.23) was determined as also the binding of 125I-labelled concanavalin A to intact cells and isolated membranes. The lysolecithin acyltransferase was found to be activated three times in microsomal membranes. The activation occurred directly after binding of concanavalin A and was temperature independent, since similar activities were found in cells treated with concanavalin A at 0 and 37 degrees C. The acyltransferase activation using increasing concentrations of concanavalin A revealed a different behaviour, as compared to the binding of concanavalin A. While the binding of concanavalin A to intact cells expressed a normal hyperbolic saturation function the activation process of the acyltransferase described a sigmoidal relationship. Correspondingly, the interaction coefficients for both functions were different (Sips coefficient for binding = 1.0 and Hill coefficient of the enzyme activation = 1.8). These results indicate that the acyltransferase activation is due to a cooperative interaction between the ligand-receptor complex and the enzyme.
mesh_terms: D008243:1-Acylglycerophosphocholine O-Acyltransferase / Q000378:metabolism*; D000217:Acyltransferases / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D002462:Cell Membrane / Q000201:enzymology; D003078:Colchicine / Q000494:pharmacology; D003208:Concanavalin A / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D005227:Fatty Acids / Q000378:metabolism; D007457:Iodine Radioisotopes; D007700:Kinetics; D008766:Methylmannosides / Q000494:pharmacology; D008861:Microsomes / Q000201:enzymology; D013601:T-Lymphocytes / Q000201:enzymology*; D013696:Temperature
chemical_list: D005227:Fatty Acids; D007457:Iodine Radioisotopes; D008766:Methylmannosides; D003208:Concanavalin A; D000217:Acyltransferases; D008243:1-Acylglycerophosphocholine O-Acyltransferase; D003078:Colchicine