Abstract
Intact human blood platelets suspended in an isoosmotic medium had no pyrophosphatase activity on inorganic pyrophosphate in the ambient fluid. In the presence of collagen sodium pyrophosphate was rapidly hydrolysed. This action was inhibited by NaF. Collagen may activate a latent inorganic pyrophosphatase (pyrophosphate phosphohydrolase, EC 3.6.1.1).