Platelets glycosylate exogenous platelet and plasma acceptors. (A) Surface galactosyltransferase activity measured by incubating platelets with GlcNAc-βGlcNAc-PAA 2.8 μm (GlcNAcβ-R + Plt) or α-Gal-Dynabead conjugates (Galα-R + Plt) and UDP-¹⁴C-galactose. Galactosyltransferase activity released into the supernatant during incubation with Dynabead conjugates (GlcNAcβ-R + Sup and Galα-R + Sup). (B) Surface sialyltransferase incorporated FITC-conjugated CMP-SA (FITC-SA) into resting (dotted line) or TRAP-activated platelets. FITC alone (Control) was added to resting (dotted line) or TRAP-activated platelets (solid line). Quantification of resting and TRAP-activated platelet-associated mean fluorescence intensity (MFI); n = 3. (C) Immunoblots of lysates from resting (Rest) or TRAP-activated platelets (TRAP), treated with FITC (C) or CMP-FITC-SA (S) or left untreated (-) with Abs to FITC, GPIbα, αIIb, and VWF. Actin is shown as a loading control (n = 3).