1awp
RAT OUTER MITOCHONDRIAL MEMBRANE CYTOCHROME B5
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OverviewOverview
When the reduction potential of cytochrome b5 is measured with the aid of, several different surface-modified electrodes that function on the basis, of electrostatic interactions with the protein, the resultant values have, been consistently more positive (40-100 mV) than the reduction potentials, measured with potentiometric methods. In this paper, we report that the, heme edge containing the exposed heme propionate, a heme methyl, and a, heme vinyl, and which constitutes part of the surface of cytochrome b5, modulates its reduction potential. The positive shifts observed in the, voltammetric measurements appear to originate from the formation of a, complex between cytochrome b5 and the modified electrode surface which (a), neutralizes the charge on the heme propionate located on the exposed heme, edge and (b) lowers the dielectric of the exposed heme microenvironment by, excluding water from the complex interface, factors which result in the, destabilization of the positive charge on the ferric heme with respect to, the neutral ferrous heme. The observed positive shift, which is induced by, complexation at the electrode surface, may indicate that similar shifts in, the reduction potential of cytochrome b5 occur when it forms a complex, with physiological partners, prior to electron transfer. The effect of the, value of the dielectric constant on the reduction potential of cytochrome, b5 was corroborated by preparing the V45L/V61L double mutant whose, reduction potential was measured to be 50 mV more negative than the value, measured for the wild type protein. The negative shift in the reduction, potential of the mutant protein was explained by the increased, accessibility of water to the heme binding site, as observed in its X-ray, crystal structure.
About this StructureAbout this Structure
1AWP is a Single protein structure of sequence from Rattus norvegicus with HEM as ligand. Full crystallographic information is available from OCA.
ReferenceReference
The reduction potential of cytochrome b5 is modulated by its exposed heme edge., Rivera M, Seetharaman R, Girdhar D, Wirtz M, Zhang X, Wang X, White S, Biochemistry. 1998 Feb 10;37(6):1485-94. PMID:9484218
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