抄録
In order to obtain the structural information around the active site of three c-type cytochromes (cyt c from horse heart, cyt c2 from Rhodospirillum rubrum, and cyt c553 from Alcaligenes xylosoxidans GIFU 1051) in aqueous solution, we studied their redox behaviors by use of the densely packed monolayer of the (S)-phenylalanine-containing CorIII complex. In the case of cyt c, no redox wave was observed, which agrees with the previous report· that the heme is buried inside of the protein. In contrast, the redox wave of cyt c2 was clearly observed, which coincides with the fact that the heme positions at the protein surface. Interestingly, in the cyclic voltammogram of cyt c2, a splitting of the wave was detected, which was elucidated to be attributable to the protonation/deprotonation of His42 imidazole of the protein. Cyt c553, of which the structural information has still not been revealed, gave the redox wave without splitting. In the light of the results of cyt c and cyt c2, this redox behavior indicates the existence of two structural characteristics for cyt c553: (i) the heme is probably located near the protein surface, and (ii) there is no conformational change caused by the protonation.
