Interaction of a ferrocenoyl-modified peptide with papain: toward protein-sensitive electrochemical probes.

A new ferrocenoyl tetrapeptide, Fc-Gly-Gly-Tyr-Arg-OH, has been synthesized, which acts as an effective competitive inhibitor to papain, with a K(i) of 9 microM at pH 6.2. The electrochemical potential of the ferrocenoyl moiety is influenced by papain binding, resulting in a small cathodic shift of 30 mV.