title: Magnetic circular dichroism used to examine the interaction of Escherichia coli cytochrome bd with ligands.
abstract: The interactions of the fully reduced and fully oxidized cytochrome bd from E. coli with ligands CO, NO, and CN- have been studied by a combination of absorption and magnetic circular dichroism (MCD) spectroscopy. In the reduced cytochrome bd, MCD resolves individual bands due to the high-spin heme b595 and the low-spin heme b558 components of the enzyme, allowing one to separately monitor their interactions along with ligand binding to the heme d component. The data show that at low concentrations, the ligands bind almost exclusively to heme d. At high concentrations, the ligands begin to interact with the low-spin heme b558. At the same time, no evidence for significant binding of the ligands to the high-spin heme b595 is revealed in either the reduced or the fully oxidized cytochrome bd complex. The data support the model [Borisov, V. B., Gennis, R. B., and Konstantinov, A. A. (1995) Biochemistry (Moscow) 60, 231-239] according to which the two high-spin hemes d and b595 share a high-affinity ligand binding site with a capacity for only a single molecule of the ligand; i.e., there is a strong negative cooperativity with respect to ligand binding to these two hemes with cytochrome d having an intrinsic ligand affinity much higher than that of heme b595.
authors.affiliation: A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Russia.
authors.forename: V
authors.initials: V
authors.lastname: Borisov
authors.forename: A M
authors.initials: AM
authors.lastname: Arutyunyan
authors.forename: J P
authors.initials: JP
authors.lastname: Osborne
authors.forename: R B
authors.initials: RB
authors.lastname: Gennis
authors.forename: A A
authors.initials: AA
authors.lastname: Konstantinov
mesh_terms: D001665:Binding Sites; D002248:Carbon Monoxide / Q000737:chemistry; D002942:Circular Dichroism; D003485:Cyanates / Q000737:chemistry; D003573:Cytochrome b Group; D003580:Cytochromes / Q000737:chemistry*; D045222:Electron Transport Chain Complex Proteins; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D006418:Heme / Q000737:chemistry; D008024:Ligands; D008280:Magnetics; D008956:Models, Chemical; D009569:Nitric Oxide / Q000737:chemistry; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry*; D013696:Temperature
chemical_list: D003485:Cyanates; D003573:Cytochrome b Group; D003580:Cytochromes; D045222:Electron Transport Chain Complex Proteins; D029968:Escherichia coli Proteins; D008024:Ligands; D009569:Nitric Oxide; D006418:Heme; D002248:Carbon Monoxide; D010088:Oxidoreductases; C040077:cytochrome bd terminal oxidase complex, E coli