Isolation of Platelet Cofactor I From Plasma and Some Properties of the Preparation

¹ From the Department of Physiology and Pharmacology, Wayne State University College of Medicine, Detroit, Michigan

A method for the purification of platelet cofactor I is described. Platelet cofactor II is first removed from plasma by adsorption on barium salts. The plasma is brought exactly to ph 6.3 for adsorbing the platelet cofactor I on kaolin, from which it is eluted at ph 7.5 with phosphate buffer. The activity is concentrated by precipitation with cold alcohol and further purified by salt fractionation. The isoelectric point of platelet cofactor I is ph 6.3–6.4. The activity is quite stable within the ph range 6–7.5 and can be preserved for many months in 50% glycerol solutions kept in a deep freeze. The protein contains less than 0.2% tyrosine, about 3.6% carbohydrate, and hexosamine. The activity is easily destroyed by heating near 30°C and above heat inactivation of solutions occurs.