Enzymic properties of the neo-plasmin-Val-442 (miniplasmin)

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Abstract

The enzymic properties of the activated plasminogen fragment (Val-442-Arg-560; S-S bridged to Val-561-Asn-790) also called miniplasmin or neo-plasmin-Val-442, were studied. This neo-plasmin was prepared by urokinase catalysed conversion of the corresponding fragment of plasminogen (Val-442-Asn-790) produced by specific limited proteolysis of native plasminogen by porcine pancreatic elastase and purified by chromatography on l-lysine-Sepharose 4B.

The kinetic parameters of hydrolysis of a number of synthetic substrates by plasmin and by ‘miniplasmin’, respectively, were found to be alike. Furthermore the inhibition by 6-aminohexanoic acid and the pH-dependence of the hydrolysis of Bz-Arg-OEt were identical for the two enzymes. It is concluded that the catalytic site of ‘miniplasmin’ is very similar to that of plasmin.

The interaction of ‘miniplasmin’ with α2-antiplasmin was studied in the presence and in the absence of 6-aminohexanoic acid. The reaction scheme which accounts satisfactorily for the reaction of plasmin with the inhibitor also fits the reaction of ‘miniplasmin’ with the inhibitor. However, it was found that ‘miniplasmin’ initially reacts with the inhibitor less readily than does plasmin, but that the rate of the second reaction step is equal to that of the corresponding step in the inhibitor-plasmin reaction. The hypothesis that site(s) other than the catalytic site of plasmin located at the NH2-terminal part of the heavy chain (residues 77–441) primarily determine the association rate of plasmin and α2-antiplasmin is supported.

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