FIG. 4.

Competition assay of STb binding to sulfatide. After sulfatide (1 μg) was immobilized on a PVDF membrane, STb (0.1 μg/ml) preincubated for 10 min with a 500-fold molar excess of either the sulfatide or galactosylceramide was added; binding of STb was measured after 10 min as described in Materials and Methods. Values represent the binding of STb to sulfatide and are the averages of duplicate experiments (three spots per experiment) analyzed by densitometry. The standard deviations from the mean are shown.