title: Thermodynamic and kinetic characterisation of individual haems in multicentre cytochromes c3.
abstract: The characterisation of individual centres in multihaem proteins is difficult due to the similarities in the redox and spectroscopic properties of the centres. NMR has been used successfully to distinguish redox centres and allow the determination of the microscopic thermodynamic parameters in several multihaem cytochromes c(3) isolated from different sulphate-reducing bacteria. In this article we show that it is also possible to discriminate the kinetic properties of individual centres in multihaem proteins, if the complete microscopic thermodynamic characterisation is available and the system displays fast intramolecular equilibration in the time scale of the kinetic experiment. The deconvolution of the kinetic traces using a model of thermodynamic control provides a reference rate constant for each haem that does not depend on driving force and can be related to structural factors. The thermodynamic characterisation of three tetrahaem cytochromes and their kinetics of reduction by sodium dithionite are reported in this paper. Thermodynamic and kinetic data were fitted simultaneously to a model to obtain microscopic reduction potentials, haem-haem and haem-proton interacting potentials, and reference rate constants for the haems. The kinetic information obtained for these cytochromes and recently published data for other multihaem cytochromes is discussed with respect to the structural factors that determine the reference rates. The accessibility for the reducing agent seems to play an important role in controlling the kinetic rates, although is clearly not the only factor.
authors: Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Rua da Quinta Grande, 6, Apt. 127, 2780-156 Oeiras, Portugal.
authors: Catarina M
authors: CM
authors: Paquete
authors: David L
authors: DL
authors: Turner
authors: Ricardo O
authors: RO
authors: Louro
authors: António V
authors: AV
authors: Xavier
authors: Teresa
authors: T
authors: Catarino
mesh_terms: D003574:Cytochrome c Group / Q000737:chemistry*; D003580:Cytochromes / Q000737:chemistry; D016969:Desulfovibrio vulgaris / Q000378:metabolism; D004579:Electron Transport; D004583:Electrons; D006418:Heme / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D010084:Oxidation-Reduction; D011522:Protons; D019163:Reducing Agents / Q000494:pharmacology; D013053:Spectrophotometry; D013696:Temperature; D013816:Thermodynamics
chemical_list: D003574:Cytochrome c Group; D003580:Cytochromes; D011522:Protons; D019163:Reducing Agents; D006418:Heme; C017165:cytochrome c(3)