Importance of protein rearrangement in the electron-transfer reaction between the physiological partners cytochrome f and plastocyanin.
Cytochrome f from turnip and plastocyanin from French bean were noninvasively cross-linked in the presence of the carbodiimide EDC so that the exposed heme edge in the former protein abuts the acidic patch remote from the copper site in the latter [Morand, L.Z., Frame, M.K., Colvert, K.K., Johnson, D.A., Krogmann, D.W., & Davis, D.J. (1989) Biochemistry 28, 8039]. The molecular mass, reduction potentials, and UV-visible and ESR spectra of the covalent complex were consistent with the composition cyt/pc and with a lack of noticeable structural perturbations of the protein molecules. Isoelectric focusing showed the presence of N-acylurea groups, byproducts of the cross-linking reaction [Zhou, J.S., Brothers, H.M. II, Neddersen, J.P., Peerey, L.M., Cotton, T.M., & Kostić, N.M. (1992) Bioconjugate Chem. 3, 382]. Laser flash spectroscopy, with riboflavin semiquinone as the reductant, showed that the electrontransfer reaction within the covalent complex cyt(II)/pc(II) is either undetectably slow or reversible. The question was resolved by monitoring, during redox titrations, the 1H NMR line widths of the heme methyl groups in free ferricytochrome f and in this protein cross-linked to plastocyanin.(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Chemistry, Iowa State University, Ames 50011.
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D003432:Cross-Linking Reagents; D003580:Cytochromes / Q000737:chemistry / Q000378:metabolism*; D045348:Cytochromes f; D004579:Electron Transport / Q000502:physiology; D007834:Lasers; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D010782:Photolysis; D010944:Plants; D010970:Plastocyanin / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D014508:Urea / Q000031:analogs & derivatives
D003432:Cross-Linking Reagents; D003580:Cytochromes; D014508:Urea; D010970:Plastocyanin; D045348:Cytochromes f