Preparation of fluorescence-labeled and cross-linked subtilisin

Streptomyces subtilisin inhibitor (SSI) is a protein characterized by both its potent inhibitory activity toward subtilisin and its structure, composed of two homologous subunits. It binds two molecules of subtilisin to form a tetrameric complex. Intermolecularly cross-linked subtilisin is expected to form a polymeric complex with SSI. This could provide a useful model of protein-protein association. Therefore, preparation of fluorescence-labeled and cross-linked subtilisin was carried out.