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Cyanide‐reactive sites in cytochrome bd complex from E. coli
Author(s) -
Krasnoselskaya Irina,
Arutjunjan Alexander M.,
Smirnova Irina,
Gennis Robert,
Konstantinov Alexander A.
Publication year - 1993
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(93)81004-j
Subject(s) - chemistry , heme , cyanide , cytochrome , autoxidation , ferric , ferrous , photochemistry , stereochemistry , hemeprotein , inorganic chemistry , enzyme , organic chemistry
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+ ‐O 2 ), 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.