Proteoglycan carrier of human platelet factor 4. Isolation and characterization

A large scale purification procedure for the human platelet factor 4 proteoglycan carrier molecule has been developed. A yield of 46% and a 33,000-fold purification have been achieved, using poly-L-lysine-Sepharose affinity column chromatography, PF4-agarose affinity column chromatography, and Bio-Gel A-0.5m gel filtration. The purified proteoglycan migrates as a single band during electrophoresis on cellulose acetate strips. A single symmetric peak was observed in sedimentation velocity analysis with an s value of 2.85. The molecular weight of the proteoglycan was determined to be 53,000 by sedimentation equilibrium. The purified proteoglycan contains 32% uronic acid, 31% galactosamine, 6.1% sulfate, and 9.9% protein. Aspartic acid, glutamic acid, leucine, glycine, and serine account for 55% of the total amino acids. The chondroitinase AC digest of the proteoglycan is sensitive to hydrolysis by chondro-4-sulfatase but not by chondro-6-sulfatase, indicating the presence of chondroitin 4-sulfate but not chondroitin 6-sulfate in the proteoglycan molecule. The interaction between this proteoglycan carrier of human PF4 and PF4 is strongly ionic strength-dependent. 0.3 M NaCl is required to dissociate the proteoglycan PF4 complex.