Acid Mucopolysaccharides As Cofactor in Formation of Platelet-clumping Substance

Incubation at 37°C for 30 min or the addition of CaCl₂ (5 mM) generated platelet-clumping activity in citrated plasma and EDTA plasma previously acidified to pH 5.5 and in which heparin was added to give a concentration of 0.5 mg/ml. Similar treatment could not produce platelet-clumping activity in saline or denatured plasma that had been heated to 56°C. Heparin, chondroitin sulfate B, or heparan sulfate produced platelet-clumping activity in BaSO₄-adsorbed serum over a given pH range. The effective pH range for each compound was; heparin 0.5 mg/ml, pH 5.16 ± 0.09 to 6.31 ± 0.14; chondroitin sulfate B 0.5 mg/ml, pH 5.62 ± 0.09 to 6.88 ± 0.06; 2 mg/ml, pH 5.17 ± 0.16 to 7.18 ± 0.16. The effect of heparan sulfate in generating platelet-clumping activity was estimated only qualitatively at pH 6.0 and proved to be positive. Chondroitin sulfate A, chondroitin sulfate C, and hyaluronic acid failed to yield platelet-clumping activity in BaSO₄-adsorbed plasma. The minimal concentrations of heparin and chondroitin sulfate B necessary to induce platelet-clumping activity in the BaSO₄-adsorbed serum were 0.5 mg/ml and 0.1 mg/ml, respectively.