Time course of sulfo-NHS-biotin inhibition of TF PCA on untreated ionomycin-treated HL-60 cells. Untreated (•) and ionomycin-treated (▪) HL-60 cells were exposed to 2 mmol/L sulfo-NHS-biotin. At the times indicated on the X-axis the reactions were terminated by the addition of excess glycine. After washing, the intact cells were stimulated with 10 μmol/L ionomycin and assayed for TF PCA. The equation y = a + bexp(−kx) was fitted to the data. Both sets of data were well described by the equation, r² = .99.