Synthetic models of the active site of cytochrome C oxidase: influence of tridentate or tetradentate copper chelates bearing a His--Tyr linkage mimic on dioxygen adduct formation by heme/Cu complexes.
Two synthetic models of the active site of cytochrome c oxidase--[(LN4-OH)CuI-FeII(TMP)]+ (1 a) and [(LN3-OH)CuI-FeII(TMP)]+ (2 a)-have been designed and synthesized. These models each contain a heme and a covalently attached copper moiety supported either by a tetradentate N4-copper chelate or by a tridentate N3-copper chelate including a moiety that acts as a mimic of the crosslinked His-Tyr component of cytochrome c oxidase. Low-temperature oxygenation reactions of these models have been investigated by spectroscopic methods including UV/Vis, resonance Raman, ESI-MS, and EPR spectroscopy. Oxygenation of the tetradentate model 1 a in MeCN and in other solvents produces a low-temperature-stable dioxygen-bridged peroxide [(LN4-OH)CuII-O2-FeIII(TMP)]+ {nuO--O=799 (16O2)/752 cm(-1) (18O2)}, while a heme superoxide species [(TMP)FeIII(O2-)CuIILN3-OH] {nuFe--O2: 576 (16O2)/551 cm(-1) (18O2)} is generated when the tridentate model 2 a is oxygenated in EtCN solution under similar experimental conditions. The coexistence of a heme superoxide species [(TMP)FeIII(O2-)CuIILN3-OH] and a bridged peroxide [(LN3-OH)CuII-O2-FeIII(TMP)]+ species in equal amounts is observed when the oxygenation reaction of 2 a is performed in CH2Cl(2)/7 % EtCN, while the percentage of the peroxide (approximately 70 %) in relation to superoxide (approximately 30 %) increases further when the crosslinked phenol moiety in 2 a is deprotonated to produce the bridged peroxide [(LN3-OH)CuII-O2-FeIII(TMP)]+ {nuO--O: 812 (16O2)/765 cm(-1) (18O2)} as the main dioxygen intermediate. The weak reducibility and decreased O2 reactivity of the tricoordinated CuI site in 2 a are responsible for the solvent-dependent formation of dioxygen adducts. The initial binding of dioxygen to the copper site en route to the formation of a bridged heme-O2-Cu intermediate by model 2 a is suggested and the deprotonated crosslinked His-Tyr moiety might contribute to enhancement of the O2 affinity of the CuI site at an early stage of the dioxygen-binding process.
Liu
Jin-Gang
JG
Institute for Materials Chemistry and Engineering, Kyushu University, Higashi-ku, Fukuoka, 812-8581, Japan.
Naruta
Yoshinori
Y
Tani
Fumito
F
D000818:Animals; D001665:Binding Sites; D040761:Biomimetic Materials / Q000737:chemistry; D002417:Cattle; D003300:Copper / Q000737:chemistry* / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D003576:Electron Transport Complex IV / Q000737:chemistry* / Q000378:metabolism; D005290:Ferric Compounds / Q000737:chemistry* / Q000378:metabolism; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D006639:Histidine / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D009206:Myocardium / Q000201:enzymology; D009942:Organometallic Compounds / Q000737:chemistry / Q000378:metabolism; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet; D013059:Spectrum Analysis, Raman; D014443:Tyrosine / Q000737:chemistry / Q000378:metabolism
D005290:Ferric Compounds; D009942:Organometallic Compounds; D014443:Tyrosine; D006418:Heme; D006639:Histidine; D003300:Copper; D003576:Electron Transport Complex IV; D010100:Oxygen