MACROMOLECULAR RECOGNITION IN THE CYTOCHROME C-CYTOCHROME-C PEROXIDASE COMPLEX INVOLVES FAST 2-DIMENSIONAL DIFFUSION

The tight binding protein complex formed by two redox partners, cytochrome c (cytc) and cytochrome c peroxidase (ccp) has been characterized by dynamic energy-transfer measurements. In Mgccp, magnesium(II) is substituted for iron(III) in the heme of ccp to produce a fluorescence energy donor, while iron(III) cytochrome c acts as an energy acceptor. At low temperatures (77 K), Mgccp shows a simple decay when free in solution but gives a complex decay when bound to the energy acceptor FeIII cytochrome c. On warming to room temperature, the decay profile is considerably simplified. This pattern suggests that molecular recognition in the protein complex produces individual conformational states which are trapped at low temperature, and reequilibrate on the subnanosecond time scale, via lower dimensional diffusion, at room temperature. © 1990 American Chemical Society.