Heparin binding peptides co-purify with glycosaminoglycans from human plasma

Glycosaminoglycans (GAGs) are complexed with plasma proteins and proteolysis of plasma reduced the protein^ GAG ratio about 140-fold. After dialysis, analysis by gradient PAGE revealed heparinase-1-sensitive GAGs, thus suggesting that heparin could be among the plasma GAGs. However, after dialysis most of the plasma GAGs were still not `free'. PAGE of peptides resistant to proteolysis showed high molecular weight bands on the two sides of the dialysis membrane despite the 3.5 kDa molecular weight cut-off. Progressive dilution of the sample allowed passage of peptides appearing as high molecular weight bands in the diffusate. We interpret this phenomenon as the presence of low molecular weight peptides that aggregate when concentrated. Peptides on both sides of the membranes bound heparin.