Abstract
Methylamine dehydrogenase (MADH), amicyanin, and cytochrome c-551i are soluble redox proteins that form a complex in solution (Chen, L., Durley, R., Mathews, F. S., and Davidson, V. L. (1994) Science 264, 86-90), which is required for the physiologic electron transfer from the tryptophan tryptophylquinone cofactor of MADH to heme via the copper center of amicyanin. The reduction of cytochrome by amicyanin within the complex in solution has been demonstrated using rapid scanning stopped-flow spectroscopy. Electron transfer from free, uncomplexed, amicyanin to cytochrome c-551i occurs much more rapidly but only to a very small extent because the reaction is thermodynamically much less favorable when amicyanin is not associated with MADH (Gray, K. A., Davidson, V. L., and Knaff, D. B. (1988) J. Biol. Chem. 263, 13987-13990). These kinetic data suggest that amicyanin binding to cytochrome c-551i occurs at different sites when amicyanin is free and when it is in complex with MADH. A model for the interactions of these proteins is presented.
Highlights
The electron transfer complex of methylamine dehydrogenase (MADH),1 amicyanin, and cytochrome c-551i from Paracoccus denitrificans is the only such physiologic complex of three weakly associating redox proteins for which a detailed crystal structure is available (Chen et al, 1994)
In vitro studies have shown that of the c-type cytochromes isolated from P. denitrificans, the most efficient electron acceptor for the Methylamine dehydrogenase (MADH)-amicyanin complex is cytochrome c-551i (Husain and Davidson, 1986)
In this paper we describe transient kinetic studies of the electron transfer reaction from amicyanin to cytochrome c-551i in which rapid scanning stopped-flow spectroscopy was used to facilitate the interpretation of the spectral changes associated with this reaction
Summary
The electron transfer complex of methylamine dehydrogenase (MADH),1 amicyanin, and cytochrome c-551i from Paracoccus denitrificans is the only such physiologic complex of three weakly associating redox proteins for which a detailed crystal structure is available (Chen et al, 1994). One would like to correlate this structural information with kinetic data on the electron transfer reactions that occur within the protein complex. Electron Transfer Complex tween reduced MADH and oxidized cytochrome c-551i in the absence of amicyanin.
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