Enzymatic activity monitoring of caspases, which are a class of cysteine protease, was performed by using peptide arrays based on surface plasmon resonance (SPR) imaging. The strategy of the detection is straightforward, using streptavidin to amplify the SPR signals of the surface-immobilized substrate peptides labeled with biotin at the C termini. Thus, the cleavage of the substrate peptides by caspases was detected as a signal decrease. Using this method, we succeeded in monitoring the activities of purified caspases and caspases in cell lysates. The SPR imaging-based peptide array would be applicable to cell-based drug screening and biochemical studies to reveal signal transduction processes.
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