The dissolution of blood clots involves hydrolysis of fibrin by the protease plasmin. Plasmin is activated by cleavage of inactive plasminogen by another protease called tissue plasminogen activator (tPA). tPA, in turn, must also be activated by proteolysis at a single site. Once plasmin is activated, it cleaves and activates more tPA in a positive feedback loop. tPA is a glycoprotein that can have either two or three N-linked oligosaccharide chains. Measurements indicate that tPA bearing two such chains is cleaved by plasmin much more rapidly than the molecule with three chains. Propose an explanation for the difference.