An ultracentrifugal approach to quantitative characterization of the molecular assembly of a physiological electron-transfer complex: the interaction of electron-transferring flavoprotein with trimethylamine dehydrogenase.

The interaction between two physiological redox partners, trimethylamine dehydrogenase and electron-transferring flavoprotein, has been characterized quantitatively by analytical ultracentrifugation at 4 degrees C. Analysis of sedimentation-equilibrium distributions obtained at 15 000 rpm for mixtures in 10 mM potassium phosphate, pH 7.5, by means of the psi function [Wills, P. R., Jacobsen, M. P. & Winzor, D. J. (1996) Biopolymers 38, 119-130] has yielded an intrinsic dissociation constant of 3-7 microM for the interaction of electron-transferring flavoprotein with two equivalent and independent sites on the homodimeric enzyme. This investigation indicates the potential of sedimentation equilibrium for the quantitative characterization of interactions between dissimilar macromolecules.