Oxidoreduction reactions involving the electrostatic and the covalent complex of cytochrome c and plastocyanin: Importance of the protein rearrangement for the intracomplex electron-transfer reaction

Journal Article · Tue Feb 21 04:00:00 EST 1989 · Biochemistry; (USA)

DOI:https://doi.org/10.1021/bi00430a065· OSTI ID:5515202

Peerey, L M; Kostic, N M ^[1]

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1. Iowa State Univ., Ames (USA)

Horse heart cytochrome c and French bean plastocyanin are cross-linked one-to-one by a carbodiimide in the same general orientation in which they associate electrostatically. The reduction potentials of the Fe and Cu atoms in the covalent diprotein complex are respectively 245 and 385 mV vs NHE; the EPR spectra of the two metals are not perturbed by cross-linking. For isomers of the covalent diprotein complex, which probably differ slightly from one another in the manner of cross-linking, are separated efficiently by cation-exchange chromatography. Stopped-flow spectrophotometric experiments with the covalent diprotein complex show that the presence of plastocyanin somewhat inhibits oxidation of ferrocytochrome c by (Fe(CN){sub 6}){sup 3{minus}} and somewhat promotes oxidation of this protein by (Fe(C{sub 5}H{sub 5}){sub 2}){sup +}. These changes in reactivity are explained in terms of electrostatic and steric effects. Pulse-radiolysis experiments with the electrostatic diprotein complex yield association constants of {ge}5 x 10{sup 6} and 1 x 10{sup 5} M{sup {minus}1} at ionic strengths of 1 and 40 mM, respectively, and the rate constant of 1.05 x 10{sup 3} s{sup {minus}1}, regardless of the ionic strength, for the intracomplex electron-transfer reaction. Analogous pulse-radiolysis experiments with each of the four isomers of the covalent diprotein complex, at ionic strengths of both 2 and 200 mM, show an absence of the intracomplex electron-transfer reaction. A rearrangement of the proteins for this reaction seems to be possible (or unnecessary) in the electrostatic complex but impossible in the covalent complex.

• DOE Contract Number: W-7405-ENG-82
• OSTI ID: 5515202
• Journal Information: Biochemistry; (USA), Journal Name: Biochemistry; (USA) Vol. 28:4; ISSN 0006-2960; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

550602* -- Medicine-- External Radiation in Diagnostics-- (1980-)
62 RADIOLOGY AND NUCLEAR MEDICINE
ANIMALS
CATIONS
CHARGED PARTICLES
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTIONS
CHEMISTRY
COPPER COMPOUNDS
CYTOCHROMES
DECOMPOSITION
ELECTRON SPIN RESONANCE
ELECTRON TRANSFER
HORSES
IMIDES
IONS
IRON COMPOUNDS
MAGNETIC RESONANCE
MAMMALS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDATION
PIGMENTS
PROTEINS
RADIATION CHEMISTRY
RADIATION EFFECTS
RADIOLYSIS
RESONANCE
SPECTROPHOTOMETRY
TRANSITION ELEMENT COMPOUNDS
VERTEBRATES