Synthetic peptide SP-2 (described in the Materials and Methods) reversed the inhibitory activity of antibody VP-1. (A) An autoradiograph of a 1.5% SDS agarose gel showing the size distribution of the R834W vWF mutant incubated with TBS (lane 1), the plasma proteinase (lane 2), the plasma proteinase in the presence of VP-1 (lane 3), and the plasma proteinase in the presence of VP-1 and 1 mmol/L SP-2. (B) Concentration dependence of SP-2 reversal of VP-1 inhibitory activity. VP-1 (90 μmol/L mouse IgG) treated with designated concentrations of SP-2 was added to the vWF mutant before the plasma proteinase. The intensity of the 200-kD band generated from the vWF was plotted against the SP-2 concentration on a log scale.