Fig. 7. Effect of pH modulation on phosphorylation of p48. Treatment of spermatozoa with acetate buffer at pH 5.5 (left panels) results in the disassembly of the MSP cytoskeleton. Labeling of the membrane with anti-p48 (red) is uniform but no antiphosphotyrosine labeling can be detected in the membrane. In cells fixed within 4 seconds after washing out the pH 5.5 buffer (middle panels), the cytoskeleton reforms along the lamellipod periphery and discrete spots of antiphosphotyrosine labeling appear along the membrane. By 60 seconds after acid removal (right panels) the cytoskeleton is completely reconstructed and spots of antiphosphotyrosine labeling are located along the lamellipodial leading edge. Bar, 10 µm. (B) Autoradiography of SDS-PAGE gels of S100 following incubation in ³²P--ATP at pH 5.5 vs pH 7.0. Labeling of p48 (arrow) is undetectable at the acidic pH.

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