FIG. 5.

Effect of HA surface density on the initial rate and final level of fusion at pH 5.7 and 37°C. Fusion of coreconstitutes containing different ratios of A/Shangdong to X-47 HAs with ghosts was measured at pH 5.7 under conditions described in the legend to Fig. 1. (A) Combination of results obtained in several independent experiments (four preparations of ghosts and virosomes; 34 fusion measurements). Error bars are ±1 standard deviation; where no error bars are visible, they are smaller than the drawn data point. Reconstitutes containing X-47 HA alone also caused a perceptible fluorescence increase at this pH under these circumstances, at a rate of 0.2 to 0.3%/min. However, considering that this is less than one-third the fusion rate at the lowest concentration of A/Shangdong (0.1 mol%) using the coreconstitutes, or less than one-fifth the rate at the next lowest concentration (0.25 mol%), no corrections were made to account for this residual X-47 activity. (B) Final levels of fusion.