A Study of the Structure of Trypsin-Like Serine Proteinases. 2. A Study of Tryptophan Fluorescence in Variants of Miniplasminogen with an Altered Primary Structure

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Abstract—Variants of miniplasminogen with an altered primary structure have been designed to study previously described changes in tryptophan fluorescence during plasminogen activation by urokinase. Miniplasminogens that contain the Trp141, Trp215, and Leu217 substitutions (the position of the amino-acid residue is specified by the Chymotrypsin nomenclature) have been tested. The activation of mutants containing a single tryptophan substitution induced changes in the fluorescence spectrum. No changes in the fluorescence spectrum were observed in the case of miniplasminogen containing a double tryptophan substitution. This indicates that both Trp141 and 215 contribute to the fluorescence spectrum shift; however, as suggested previously, the contribution of changes in the Trp215 microenvironment is greater. The Trp141, Trp215, and Leu217 amino-acid substitutions in miniplasminogen have no effect on the rate of plasminogen activation by urokinase. The replacement of the conserved Trp215 residue in serine proteases led to a significant reduction but not loss of the amidolytic activity of plasmin.