Human PAI-1with NBD labeled at the scissile bond of the reactive loop. PAI-1 NBD-P1\' was created by mutagenesis of the P1\' serine residue (Ser347) at the P1-P1\' scissile bond to cysteine. This provided a free thiol group for NBD labeling, a fluorescent probe highly sensitive to changes in dissolution and hydrophobic environment. The fluorescence emission of PAI-1 NBD-P1\' is quenched upon cleavage of the reactive center loop by a target protease.
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