Antagonistic effects of hydrostatic pressure and osmotic pressure on cytochrome P-450cam spin transition.

The combined effects of hydrostatic pressure and osmotic pressure, generated by polyols, on the spin equilibrium of fenchone-bound cytochrome P-450cam were investigated. Hydrostatic pressure indices a high spin to low spin transition, whereas polyols induce the reversed reaction. Of the four solutes used, glycerol, glucose, stachyose, and sucrose, only the last two would act on the spin transition by osmotic stress.

Electrostatic control of the substrate access channel in cytochrome P-450cam.

Camphor binding to ferric cytochrome P-450cam is a two-step process. The first step corresponds to the diffusion of camphor into the heme pocket, and the second one corresponds to an observable spin transition of the heme iron. In this paper, electrostatic interactions that may control the opening of the structure to allow substrate access to the buried and not solvent-exposed active site were examined.

Effects of monovalent cations on cytochrome P-450 camphor. Evidence for preferential binding of potassium.

Binding of monovalent cations of increasing ionic radius to ferric cytochrome P-450cam was measured. Potassium has the highest affinity for the cation binding site observed in the X-ray crystallographic structure with Kdcat = 12 mM, compared with the smaller cation lithium, (Kdcat = 37 mM) and the larger cation cesium (Kd cat = 20 mM). Coupling between cation binding and camphor binding is established by the observation of a linear relationship between the corresponding binding free energies.

Osmotic regulation of gene action.

Most reactions involved in gene translation systems are ionic-dependent and may be explained in electrostatic terms. However, a number of observations of equilibria and rate processes making up the overall reactions clearly indicate that there is still an enormous gap between the rough picture of the mechanism of ionic regulation and the detailed behavior of reactions at the molecular level that hold the key to specific mechanisms. The present paper deals with possible osmotic contributions arising from the gel state of gene systems that are complementary to, and interdependent of, electrostatic contributions.

Conformational dynamics of cytochrome P-450cam as monitored by photoacoustic calorimetry.

Conformational transitions of cytochrome P-450cam following the dissociation of CO from the ferrous heme were investigated by using photoacoustic calorimetry. The effect of substrate association on the acoustic signal was also examined. Results show that the conformational dynamics of cytochrome P-450cam substrate-free protein occur faster than 10 ns, which is the time scale of the instrument response.