Activated platelets release soluble glycosyltransferases. GalNAc-, Gal-, and sialyltransferase activities in ultracentrifuged supernatant (S) from TRAP-activated platelets and detergent lysates of resting platelets (P). Glycosyltransferase activities were measured using C¹⁴-labeled donor sugars and enzyme-specific acceptor substrates (n = 3-4).