Intramolecular Electron Transfer of CytochromecModified withN,N,N′,N″,N″-Diethylenetriaminepentaacetatocobaltate(III)

Keiichi Tsukahara, Nao Iida, Yuka Kaida, Hiroshi Takashima, Maya Mizobe, Ryuichi Arakawa
2003 Bulletin of the Chemical Society of Japan  
Horse heart cytochrome c (cytc) modified with an N,N,N 0 ,N 00 ,N 00 -diethylenetriaminepentaacetatocobaltate(c) ion, [cytc c {Co c (dtpa)}], was prepared and characterized. The major component of singly modified [cytc c {Co c (dtpa)}] contains a [Co c (dtpa)] ion at Lys13, of which the "-amino group is linked with a carboxylate ion of dtpa. A oneelectron reduced protein, [cytc b {Co c (dtpa)}], was prepared by reduction with a methylviologen-radical cation, which was produced in situ by a
more » ... reduction using a tris(2,2 0 -bipyridine)ruthenium(b) ion in the presence of disodium dihydrogen ethylenediaminetetraacetate at 25 C, pH 7.5 (0.010 mol dm À3 tris(hydroxymethyl)aminomethane-HCl buffer), and an ionic strength of 0.50 mol dm À3 (NaCl). The reaction of [cytc b {Co c (dtpa)}] to form [cytc c {Co b -(dtpa)}] was very slow, and was followed by conventional spectrophotometry. The reaction was of first order in the protein and the first-order rate constant (ð3:1 AE 0:5Þ Â 10 À4 s À1 ) was independent of the concentration of the protein, indicating that the intramolecular electron-transfer (ET) process is predominant. The reaction mechanism is discussed on a through-bond or through-space pathway. The slow intramolecular ET rate might arise not only from the long distance, but also from the large reorganization energy for the Co(c)/Co(b) couple.
doi:10.1246/bcsj.76.1323 fatcat:tavrq2djuzaillbgdmcxug2yja