Specific aspects of electron transfer from adrenodoxin to cytochromes p450scc and p45011beta.

An analysis of the electron transfer kinetics from the reduced [2Fe-2S] center of bovine adrenodoxin and its mutants to the natural electron acceptors, cytochromes P450scc and P45011beta, is the primary focus of this paper. A series of mutant proteins with distinctive structural parameters such as redox potential, microenvironment of the iron-sulfur cluster, electrostatic properties, and conformational stability was used to provide more detailed insight into the contribution of the electronic and conformational states of adrenodoxin to the driving forces of the complex formation of reduced adrenodoxin with cytochromes P450scc and P45011beta and electron transfer. The apparent rate constants of P450scc reduction were generally proportional to the adrenodoxin redox potential under conditions in which the protein-protein interactions were not affected. However, the effect of redox potential differences was shown to be masked by structural and electrostatic effects. In contrast, no correlation of the reduction rates of P45011beta with the redox potential of adrenodoxin mutants was found. Compared with the interaction with P450scc, however, the hydrophobic protein region between the iron-sulfur cluster and the acidic site on the surface of adrenodoxin seems to play an important role for precise complementarity in the tightly associated complex with P45011beta.