MAGNETIC AND MODEL STUDIES OF CYTOCHROME C OXIDASE

[摘要] Part I. Magnetochemical Studies of Bovine Cytochrome c Oxidase. The variable-temperature (20-200 K) magnetic susceptibility properties of bovine cytochrome c oxidase in its fully-oxidized or resting state (Hartzell-Beinert and Yonetani preparations), its fully-reduced state (Hartzell-Beinert) and its resting(.)CN(;;-) state (Hartzell-Beinert and Yonetani) have been examined. In general, the magnetochemical results for the Hartzell-Beinert (g(,12) and g(,12)-less) and Yonetani resting enzyme forms are nearly Curie in nature and identical to those of Tweedle. All three sets of data are consistent with a strong antiferromagnetic exchange-coupled pair at the active site with -J (GREATERTHEQ) 200cm(;;-1) to give a epr inactive S = 2 ground state. The Hartzell-Beinert reduced enzyme displays magnetochemical behavior like that previously reported by Tweedle, where only cyt.a(,3)(;;2+) (S = 2) is a paramagnetic center. Finally, the magnetochemistry of the Hartzell-Beinert and Yonetani resting(.)CN(;;-) derivatives were also found to be nearly identical to that of Tweedle, in that the data are non-Curie in nature and can be interpreted in terms of a weak antiferromagnetic exchange-coupled pair at the active site. Part II. A Synthetic Model Compound Approach to the Active Site Structure of Cytochrome c Oxidase. Twelve new (mu)-imidazolato heterobinuclear metal complexes have been synthesized to model the proposed imidazolate-bridged cyt.a(,3)(;;3+)(imid)Cu(,U)(;;2+) active site structure of resting cytochrome c oxidase where -J(,(Fe(;;III)-Cu(;;II))) (GREATERTHEQ) 200 cm(;;-1) may be the case. The model compounds have been derived from LFe(;;III)(TPP) (TPP(;;2-) = tetraphenylporphyrinato and L = OSO(,2)CF(,3)(;;-)) and M;;(;;II)(2-meimidH)(,2)DAP (;;2+) or M;;(;;II)(imidH)(,2)DAP (;;2+) (M;;(;;II) = Zn and Cu) to yield 12 species. The variable-temperature (ca. 20-200 K) magnetochemical and epr (10 K) data obtained indicate that the Fe(III) and Cu(II) centers in compound 2 and Co(II) and Cu(II) centers in compounds 6 and 8 are electronically isolated from one another with -J (TURN) 0 cm(;;-1). Compound 4 exhibits magnetochemcial and epr spectral properties consistent with strong antiferromagnetic coupling between Fe(III) (S = 5/2, 1/2) and Cu(II) (S = 1/2) where -J(,(Fe(;;III)-Cu(;;II))) (GREATERTHEQ) 200 cm(;;-1). Compounds 10 and 12 also display variable-temperature magnetochemical and epr spectral behavior consistent with a strong antiferromagnetic exchange-coupled Mn(;;II)(S = 5/2)(imid)Cu(;;II)(S = 1/2) (;;+) pair with -J (GREATERTHEQ) 200 cm(;;-1) to give a resultant epr inactive S = 2 ground state. As such, these model compounds may be considered to be good spin mimics of the cyt.a(,3)(;;3+)(S = 5/2)- Cu(,U)(;;2+)(S = 1/2) active site of cytochrome c oxidase in its resting state. (Abstract shortened with permission of author.)

[发布机构] Rice University