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°C. Analysis of sedimentation‐equilibrium distributions obtained at 15000 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, 119–1301 has yielded an intrinsic dissociation constant of 3–7 μM 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.