KINETICS OF SENDAI VIRUS ENVELOPE FUSION WITH ERYTHROCYTE-MEMBRANES AND VIRUS-INDUCED HEMOLYSIS

The kinetics of fusion of the Sendai virus envelope with erythrocyte membranes were studied by spin-label electron spin resonance (ESR). The virion envelope lipid bilayer was labeled with nitroxide derivatives of phosphatidylcholine and phosphatidylethanolamine. As the virus envelope fuses with the erythrocyte membrane, the viral lipids diffuse into the cellular lipid bilayer and the spin-label spectrum changes from that characteristic of virus to that of the erythrocyte. The ESR spectral changes can be quantitatively related to the fraction of spin-labeled virus fused with the erythrocyte membrane. The fusion process was found to follow the form of a first-order reaction with a half-time of 7 ± 1 min at 37 °C that is independent of virus concentration. The kinetics of the viral hemolytic activity were studied by spin-label ESR as changes in erythrocyte bilayer fluidity induced by hemolysis. The half-time of the hemolytic reaction is similar to that of envelope fusion and is independent of virus concentration at submaximal levels of hemolysis, suggesting that envelope fusion is the rate-limiting step in hemolysis under conditions of active hemolysis. However, virions with very low hemolytic activity, prepared by harvesting virus early after infection, lyse erythrocytes much more slowly, even though they fuse with erythrocyte membranes as efficiently as normal virus. Different strains of Sendai virus vary in their envelope-fusing activity, and these differences are correlated with their ability to fuse erythrocytes with each other. © 1979, American Chemical Society. All rights reserved.