title: Studies on the nature of the catalytically essential ionizing group of plasmin with pK 8.4.
abstract: A fully carbamylated derivative of plasminogen having no free amino groups has been prepared and converted by urokinase to an active enzyme, called carbamyl plasmin A, with a single free NH2-terminal amino group (Val-561). Carbamyl plasmin A was shown to possess a catalytically essential ionizing group having pK 8.6. Carbamylation of the free NH2-terminal amino group of carbamyl plasmin A led to complete loss of catalytic activity. The results of solvent perturbation studies of normal plasmin (EC 3.4.21.7) indicate that the group with pK 8.4 is a neutral acid group. It is suggested that the catalytically essential ionizing group of plasmin having a pK of 8.4 is the alpha-ammonium group of the NH2-terminal Val-561 or the light chain of plasmin, forming an ion pair with a COO- group of an aspartate or glutamate residue.
mesh_terms: D002219:Carbamates; D005341:Fibrinolysin / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008722:Methods; D010958:Plasminogen
chemical_list: D002219:Carbamates; D010958:Plasminogen; D005341:Fibrinolysin; C021776:carbamyl plasmin A