The reciprocal effects of epsilon-aminohexanoic acid and chloride ion on the activation of human [Glu1]plasminogen by human urokinase.
The activation of human [Glu1]plasminogen [( Glu1]Pg) by high-molecular-weight two-chain human urinary urokinase [EC 3.4.21.31) and low-molecular-weight two-chain human urinary urokinase is inhibited by Cl- at physiological concentrations and stimulated by epsilon-aminohexanoic acid (epsilon Ahx; epsilon-aminocaproic acid). The inhibition by Cl- does not occur in the presence of concentrations of epsilon Ahx that saturate the acid's weak binding sites on [Glu1]Pg, and the stimulation by epsilon Ahx is maximally exhibited in the presence of Cl-. We have used intrinsic fluorescence measurements with [Glu1]Pg to show that the conformational alteration and the concomitant increase in activation rate that accompanies epsilon Ahx-binding to [Glu1]Pg in the presence of Cl- does not occur in the same manner without Cl-. Further, the decrease in the intrinsic fluorescence that is attendant to Cl- binding to [Glu1]Pg in the absence of epsilon Ahx is not observed in the presence of this effector molecule. Analyses of the results of this manuscript strongly indicate that a conformation of [Glu1]Pg that is not optimal for its activation by urokinase is adopted in the presence of Cl-, and this is relieved by epsilon Ahx. This has important implications in the inhibition of [Glu1]Pg activation in the solution phase of blood plasma and in the large acceleration of this process when plasminogen is bound to physiological positive effectors via its epsilon Ahx-binding site(s).
Urano
T
T
Chibber
B A
BA
Castellino
F J
FJ
D000614:Aminocaproates / Q000494:pharmacology*; D015119:Aminocaproic Acid / Q000494:pharmacology*; D002712:Chlorides / Q000494:pharmacology*; D004789:Enzyme Activation; D006801:Humans; D007700:Kinetics; D008970:Molecular Weight; D010958:Plasminogen / Q000302:isolation & purification / Q000378:metabolism*; D014568:Urokinase-Type Plasminogen Activator / Q000378:metabolism* / Q000652:urine
D000614:Aminocaproates; D002712:Chlorides; D010958:Plasminogen; D014568:Urokinase-Type Plasminogen Activator; D015119:Aminocaproic Acid