Cyanide‐reactive sites in cytochrome bd complex from E. coli

FEBS Letters

Gennis, Robert²  Arutjunjan, Alexander M.¹  Krasnoselskaya, Irina¹  Smirnova, Irina¹  Konstantinov, Alexander A.¹ 

[1]A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119899, Russian Federation

[2]School of Chemical Sciences, University of Illinois at Urbana-Champain, Urbana, IL, USA

关键词: Cytochrome bd;    Magnetic circular dichroism;    Cyanide binding;    Bacterial oxidases;    Heme-heme interactions;    E. coli;    MCD;    magnetic circular dichroism;   

DOI  :  10.1016/0014-5793(93)81004-J

学科分类：生物化学/生物物理

来源: John Wiley & Sons Ltd.

【 摘 要 】

Cyanide reacts with cytochrome bd from E. coli in an ‘aerobically oxidized’ state (mainly, an oxygenated complex b ₅₅₈ ³⁺ b ₅₉₅ ³⁺ d ²⁺-O₂), bringing about (i) decomposition of the heme d ²⁺ oxycomplex (decay of the 648 nm absorption band) and (ii) extensive red shift in the Soret region accompanied by minor changes in the visible range assigned to ferric heme b ₅₉₅. MCD spectra show that the Soret red shift is associated with heme b ₅₅₈ ³⁺ high-to low-spin transition. This is the first unambiguous demonstration that heme b ₅₉₅ can bind exogenous ligands. No reaction of cyanide with b ₅₅₈ is observed. In about 70% of the enzyme which forms the cyano complex, the spin-state transition of b ₅₉₅ decay of heme d oxycomplex match each other kinetically (k _eff ca. 0.002 s⁻¹ at 50 mM KCN, pH 8.1, 25°C). This points to an interaction between the two hemes. The concerted binding of cyanide to d ³⁺ and b ₅₉₅ ³⁺, perhaps as a bridging ligand, is probably rate-limited by d ²⁺ oxycomplex autoxidation. In the remaining 30% of the isolated bd, there is a rapid phase of cyanide-induced b ₅₉₅ spin-state transition which can be tentatively assigned to that proportion of the enzyme in which heme d is initially in the ferric rather than ferrous-oxy form.

【 授权许可】

Unknown