Lateral mobility of phospholipids in turkey erythrocytes. Implications for adenylate cyclase activation

Abstract

Hormone activation of turkey erythrocyte adenylate cyclase is affected by temperature and by cis-vaccenic acid incorporation. This was correlated with changes in membrane "fluidity" which were previously assumed to affect lateral diffusion of the beta-adrenergic receptor (Rimon, G., Hanski, E., and Levitzki, A. (1980) Biochemistry 19, 4451-4460; Briggs, M. M., and Lefkowitz, R. J. (1980) Biochemistry 19, 4461-4466). To test this hypothesis, we measured the lateral mobility of the fluorescent phospholipid N-4-nitrobenzo-2-oxa-1,3-diazolyl-phosphatidylethanolamine (NBD-PE in turkey erythrocyte ghosts, using fluorescence photobleaching recovery. Ghosts labeled only in the external leaflet exhibited a linear Arrhenius plot of the lateral diffusion coefficient (D) with little change in the mobile fraction of NBD-PE between 45 and 5 degrees C. Labeling from both sides, however, yielded a break point (approximately 30 degrees C) in the Arrhenius plot and a 30% decrease in the mobile fraction of NBD-PE from 24 to 10 degrees C, indicating differences between the external and inner monolayers. The observed discontinuities are not due to gel-phase formation, since fluorescence depolarization of cis- and transparinaric acid did not reveal discontinuities at this temperature range. cis-Vaccenic acid incorporation did not markedly affect either D or the mobile fraction of NBD-PE at 25 degrees C. These results are discussed in view of the effects of temperature and cis-vaccenic acid incorporation on adenylate cyclase activation.