Conversion of cholesterol to pregnenolone mobilizes cytochrome P-450 in the inner membrane of adrenocortical mitochondria: protein rotation study. 1990

Y Ohta, and F Mitani, and Y Ishimura, and K Yanagibashi, and M Kawamura, and S Kawato
Institute of Physics, College of Arts and Sciences, University of Tokyo at Komaba.

Rotation of cytochrome P-450 was examined in bovine adrenocortical mitochondria before and after an enzymatic transformation of cholesterol into pregnenolone by cytochrome P-450scc in the presence of malate. Rotational diffusion was measured by observing the decay of absorption anisotropy, r(t), after photolysis of the heme.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 substrate-dependent intermolecular interactions of cytochrome P-450 with other redox components. Rotational mobility of cytochrome P-450 was significantly dependent on the decrease in cholesterol content by side chain cleavage reaction catalyzed by cytochrome P-450scc. In a typical experiment, the observed value for the normalized time-independent anisotropy r(infinity)/r(0) was decreased from 0.78 in control mitochondria to 0.60 after conversion of 21% of cholesterol to pregnenolone, while no significant change was observed for the average rotational relaxation time phi of about 700 microseconds. Significantly high values of r(infinity)/r(0) = 0.78 and 0.60 imply co-existence of mobile and immobile populations of cytochrome P-450. Since we observed that the heme angle tilted 55 degrees from membrane plane, 22% (control mitochondria) and 40% (after conversion of cholesterol to pregnenolone) of cytochrome P-450 in mitochondria are calculated to be mobile in the preparation. The significant mobilization of cytochrome P-450scc molecules caused by the conversion of cholesterol to pregnenolone is likely due to changes in protein-protein interactions with its redox partners, since the lipid fluidity was kept unchanged by the cholesterol depletion.(ABSTRACT TRUNCATED AT 250 WORDS)

UI MeSH Term Description Entries
D007425 Intracellular Membranes Thin structures that encapsulate subcellular structures or ORGANELLES in EUKARYOTIC CELLS. They include a variety of membranes associated with the CELL NUCLEUS; the MITOCHONDRIA; the GOLGI APPARATUS; the ENDOPLASMIC RETICULUM; LYSOSOMES; PLASTIDS; and VACUOLES. Membranes, Intracellular,Intracellular Membrane,Membrane, Intracellular
D008560 Membrane Fluidity The motion of phospholipid molecules within the lipid bilayer, dependent on the classes of phospholipids present, their fatty acid composition and degree of unsaturation of the acyl chains, the cholesterol concentration, and temperature. Bilayer Fluidity,Bilayer Fluidities,Fluidities, Bilayer,Fluidities, Membrane,Fluidity, Bilayer,Fluidity, Membrane,Membrane Fluidities
D008928 Mitochondria Semiautonomous, self-reproducing organelles that occur in the cytoplasm of all cells of most, but not all, eukaryotes. Each mitochondrion is surrounded by a double limiting membrane. The inner membrane is highly invaginated, and its projections are called cristae. Mitochondria are the sites of the reactions of oxidative phosphorylation, which result in the formation of ATP. They contain distinctive RIBOSOMES, transfer RNAs (RNA, TRANSFER); AMINO ACYL T RNA SYNTHETASES; and elongation and termination factors. Mitochondria depend upon genes within the nucleus of the cells in which they reside for many essential messenger RNAs (RNA, MESSENGER). Mitochondria are believed to have arisen from aerobic bacteria that established a symbiotic relationship with primitive protoeukaryotes. (King & Stansfield, A Dictionary of Genetics, 4th ed) Mitochondrial Contraction,Mitochondrion,Contraction, Mitochondrial,Contractions, Mitochondrial,Mitochondrial Contractions
D008956 Models, Chemical Theoretical representations that simulate the behavior or activity of chemical processes or phenomena; includes the use of mathematical equations, computers, and other electronic equipment. Chemical Models,Chemical Model,Model, Chemical
D011284 Pregnenolone A 21-carbon steroid, derived from CHOLESTEROL and found in steroid hormone-producing tissues. Pregnenolone is the precursor to GONADAL STEROID HORMONES and the adrenal CORTICOSTEROIDS. 5-Pregnen-3-beta-ol-20-one,5 Pregnen 3 beta ol 20 one
D002417 Cattle Domesticated bovine animals of the genus Bos, usually kept on a farm or ranch and used for the production of meat or dairy products or for heavy labor. Beef Cow,Bos grunniens,Bos indicus,Bos indicus Cattle,Bos taurus,Cow,Cow, Domestic,Dairy Cow,Holstein Cow,Indicine Cattle,Taurine Cattle,Taurus Cattle,Yak,Zebu,Beef Cows,Bos indicus Cattles,Cattle, Bos indicus,Cattle, Indicine,Cattle, Taurine,Cattle, Taurus,Cattles, Bos indicus,Cattles, Indicine,Cattles, Taurine,Cattles, Taurus,Cow, Beef,Cow, Dairy,Cow, Holstein,Cows,Dairy Cows,Domestic Cow,Domestic Cows,Indicine Cattles,Taurine Cattles,Taurus Cattles,Yaks,Zebus
D002784 Cholesterol The principal sterol of all higher animals, distributed in body tissues, especially the brain and spinal cord, and in animal fats and oils. Epicholesterol
D002786 Cholesterol Side-Chain Cleavage Enzyme A mitochondrial cytochrome P450 enzyme that catalyzes the side-chain cleavage of C27 cholesterol to C21 pregnenolone in the presence of molecular oxygen and NADPH-FERRIHEMOPROTEIN REDUCTASE. This enzyme, encoded by CYP11A1 gene, catalyzes the breakage between C20 and C22 which is the initial and rate-limiting step in the biosynthesis of various gonadal and adrenal steroid hormones. CYP11A1,Cholesterol Desmolase,Cholesterol Monooxygenase (Side-Chain-Cleaving),Cytochrome P-450 CYP11A1,Cytochrome P-450(scc),20,22-Desmolase,CYP 11A1,Cytochrome P450 11A1,Cytochrome P450scc,20,22 Desmolase,Cholesterol Side Chain Cleavage Enzyme,Cytochrome P 450 CYP11A1
D004058 Diffusion The tendency of a gas or solute to pass from a point of higher pressure or concentration to a point of lower pressure or concentration and to distribute itself throughout the available space. Diffusion, especially FACILITATED DIFFUSION, is a major mechanism of BIOLOGICAL TRANSPORT. Diffusions
D005287 Ferredoxin-NADP Reductase An enzyme that catalyzes the oxidation and reduction of FERREDOXIN or ADRENODOXIN in the presence of NADP. EC 1.18.1.2 was formerly listed as EC 1.6.7.1 and EC 1.6.99.4. Adrenodoxin Reductase,Iron-Sulfur Protein Reductase,NADPH-Ferredoxin Reductase,Ferredoxin NADP Reductase,Iron Sulfur Protein Reductase,NADPH Ferredoxin Reductase,Protein Reductase, Iron-Sulfur,Reductase, Adrenodoxin,Reductase, Ferredoxin-NADP,Reductase, Iron-Sulfur Protein,Reductase, NADPH-Ferredoxin

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