Photo cross-linking of a serotonin conjugate to COAT-platelets.

B-BSA-(5-HT)₆ conjugated with 4-azido-2,3,5,6-tetrafluorobenzoic acid was used in COAT-platelet production7 as described in “Materials and methods.” (A) After activation, cells were UV irradiated, lysed, partially digested with chymotrypsin, and added to microtiter plates coated with antibodies against platelet α-granule proteins: fibrinogen (Fbg), thrombospondin (Tsp), fibronectin (Fn), von Willebrand factor (VWF), factor V, and α₂-antiplasmin (AP). Bound biotin was detected with streptavidin-peroxidase. (B) A more extensive examination of b-BSA-(5-HT)₆ cross-linking to Fbg and Tsp. Ionophore/thrombin (A/T)–activated, thrombin (T)–activated, and control platelets were analyzed with and without photo cross-linking. Biotin bound to either anti-Fbg or anti-Tsp was detected as in the previous panel.