Ruthenium (II) complex of mesoporphyrin-IX was incorporated into apomyoglobin to prepare artificial ruthenium myoglobin (RuMb) containing the ruthenium porphyrin in place of protoheme. The electrochemical and spectral characteristics (i.e., UV and CD spectra) of RuMb were investigated in comparison with wild type myoglobin. The effect of the metal center on the redox properties of myoglobin is directly observed by electrochemical analysis, all of which may be compared with similar measurements of the wild type myoglobin. Unlike other metal reconstituted myoglobins, i.e., cobalt myoglobin and manganese myoglobin, fast and reversible electron transfer properties were observed for RuMb, which is comparable with wild type myoglobin. The formal potential of 170 (+/-10) mV vs. Ag|AgCl (sat. KCl) of RuMb was directly determined for the first time by cyclic voltammetry, where the k(0)' value was estimated to be about 3(+/-0.2)x10(-4) cm s(-1) at pH 6.8. Mediatorless and reversible spectroelectrochemical behaviors were also observed using an optically transparent thin-layer electrode cell (OTTLE). The present results suggest that the major redox properties of the protein result from both the metal porphyrin center and globin environment. The novel redox properties predict that the engineered RuMb has analogous biofunctionalities to the wild type myoglobin in contrast to other metal reconstituted myoglobins.