FIG. 4.

Effect of inactivation of HA from A/Shangdong at pH 5.6 on X-47-mediated fusion at pH 5.1. Coreconstitutes containing HAs from both strains of virus were prepared at a 9:1 or 1:9 (X-47-to-A/Shangdong) molar ratio as described in Materials and Methods. Ten nanomoles of virosomes was preincubated in a small volume of buffer at pH 5.6 in the absence of target membranes for 15 min at 37°C. Subsequently, the rate of fusion was measured at pH 5.1 and 37°C (dark bars) and compared to the initial rate of the corresponding untreated coreconstitutes measured under the same conditions (hatched bars).