EM localization of gold-conjugated thrombin in COSdel.238 cells. Cells were preincubated with gold-complexed thrombin as in Fig 6 and exposed to 37°C for 0, 10, and 45 minutes (A, B, and C, respectively). Gold particles remained distributed on the cell surface during this period (arrowheads), with only a rare intracellular particle found (arrow).