Specificity of biotin-PK binding to HUVECs in the presence of added HK. (A) The effect of MoAbs to HK and PK on the binding of biotin-PK to HUVECs preincubated with 20 nmol/L HK. Binding of biotin-PK to HUVECs was measured in the presence of 1- to 10-fold molar excess of the MoAbs, HKL13 (□), HKL16 (⋄), or PK6 (○). Binding of biotin-PK in the presence of the antibodies is expressed as a percentage of the binding in their absence. The data presented are the mean ± SEM of three experiments. (B) PK and biotin-PK compete for binding to HUVECs. HUVECs pretreated with 20 nmol/L HK were incubated with 20 nmol/L biotin-PK in the presence of 10 to 2,000 nmol/L PK. Binding of biotin-PK in the presence of PK is expressed as a percentage of its binding in the absence of PK. The data shown are the mean ± SEM of three experiments. The absence of standard error bars at some points indicates that the variation was too low to indicate visually.