title: Rotation and protein-protein interactions of cytochrome P-450 in the inner membrane of adrenocortical mitochondria.
abstract: Rotational diffusion of the total cytochrome P-450 (P-450scc plus P-45011 beta) in bovine adrenocortical mitochondria was examined by observing the decay of absorption anisotropy, r(t), after photolysis of the hemo.CO complex by a vertically polarized laser flash. Analysis of r(t) was based on a "rotation-about-membrane normal" model. The measurements were used to investigate intermolecular interactions of cytochrome P-450 with other membrane proteins. The absorption anisotropy decayed within 1 ms to a time-independent value. Rotational diffusion of cytochrome P-450 was dependent on the presence and absence of deoxycorticosterone (DOC), a substrate for cytochrome P-45011 beta. The observed value for the normalized time-independent anisotropy r(infinity)/r(0) and the average rotational relaxation time phi are r(infinity)/r(0) = 0.88 and phi = 233 microseconds when DOC is absent, and r(infinity)/r(0) = 0.65 and phi = 350 microseconds when DOC is present. Judging from the phi value, rotating P-450 is not a monomeric molecule, but would be a small microaggregate with an average diameter of about 120 A. A significantly high value of r(infinity)/r(0) implies co-existence immobile populations of cytochrome P-450. Based on the assumption that the heme angle tilts 55 degrees from the membrane plane (Gut et al. (1983) J. Biol. Chem. 258, 8588-8594), 65% (when DOC is present) or 88% (when DOC is absent) of cytochrome P-450 in mitochondria is immobilized within the experimental time range of 2 ms due to the presence of immobile protein microaggregates.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Institute of Physics, College of Arts and Sciences, University of Tokyo, Komaba.
authors.forename: S
authors.initials: S
authors.lastname: Kawato
authors.forename: F
authors.initials: F
authors.lastname: Mitani
authors.forename: T
authors.initials: T
authors.lastname: Iizuka
authors.forename: Y
authors.initials: Y
authors.lastname: Ishimura
mesh_terms: D000302:Adrenal Cortex / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004058:Diffusion; D007700:Kinetics; D008565:Membrane Proteins / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D012399:Rotation; D013053:Spectrophotometry
chemical_list: D008565:Membrane Proteins; D003577:Cytochrome P-450 Enzyme System