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At least 1,333 records · Page 74Linked to original sources
PubMed1989

Magnetic circular dichroism studies of the active site structure of hemoprotein H-450: comparison to cytochrome P-450 and sensitivity to pH effects.

Ferric, ferrous and ferrous-CO hemoprotein H-450 from rat liver have been examined with magnetic circular dichroism spectroscopy under alkaline (pH 8.0) and acidic (pH 6.0) conditions. The spectral properties of these species require that one of the axial heme iron ligands in the alkaline ferric and ferrous states must be a thiolate sulfur, presumably from cysteine. The data are most consistent with the ligand trans to thiolate being either histidine or methionine. The reversible pH effects on the spectral properties of the ferrous protein, but not of the ferric protein, appear to involve protonation or displacement of the thiolate. As treatment of the ferrous protein with CO does not yield a thiolate-ligated ferrous-CO adduct, CO either displaces the thiolate or its addition is accompanied by protonation of the thiolate.

Animals↗
PubMed1992

Ethylbenzene hydroxylation by cytochrome P450cam.

The metabolism of ethylbenzene by cytochrome P450cam was analyzed by experimental and theoretical methods. The present experiments indicate that ethylbenzene is hydroxylated almost exclusively at the secondary ethyl carbon with about a 2:1 ratio of R:S product. Several molecular dynamics trajectories were performed with different starting conformations of ethylbenzene in the active site of P450cam. The stereochemistry of hydroxylation predicted from the molecular dynamics simulations was found to be in good agreement with the observed products.

Benzene Derivatives↗
PubMed1983

Intracellular recordings from salamander olfactory receptor cells.

Intracellular recordings were obtained from salamander olfactory receptor cells. The occurrence of an intracellular spike in response to the antidromic stimulation of the olfactory fibers was considered as a physiological criterion of a neuronal impalement. The mean resting potential was -56 +/- 9 mV (mean +/- S.D.; n = 70). Fifty-two cells presented a spontaneous spike activity lower than 2 impulses/s. Appropriate olfactory stimulation generally evoked a slow and graded decrease (up to 28 mV) of the intracellular potential. The input resistance of the cell decreased markedly during the response. The slow potential change induced a repetitive firing. Increasing the intensity of the olfactory stimulation increased the instantaneous frequency of firing (up to 25 s-1) and reduced the spike amplitude. The spikes presented an inflexion in the rising phase indicating a two-stage depolarization. With the strongest intensities of stimulation the impulse activity was stopped during the repolarizing phase of the cell response when the membrane potential was still appreciably depolarized.

Animals↗
PubMed1991

EPR-spectroscopy of reduced oxyferrous-P450cam.

X-irradiation of the ternary complex of P450:substrate:O2 at 77 K produces a reduced intermediate by electron addition to the Fe:O2 complex which can be studied by EPR-spectroscopy. The EPR spectrum of the new species exhibits rhombic symmetry with g-factors of 2.27, 2.17 and 1.95, respectively. Increasing the temperature of the sample to 190 K results in loss of intensity of the intermediate signals. X-irradiation of oxymyo- and oxyhemoglobin produces similar EPR signals indicating that the added electron is resident on the Fe:O2 compleX (Kappl, R., et al. (1985) Biochim. Biophys. Acta 870, 20-30).

Camphor 5-Monooxygenase↗
PubMed1993

Essential role of the Arg112 residue of cytochrome P450cam for electron transfer from reduced putidaredoxin.

Cytochrome P450cam (CYP101) of Pseudomonas putida PpG1 in which Arg112 is substituted by Cys was isolated by in vitro random mutagenesis of the camC gene DNA coding for P450cam. The absorption spectra of the purified mutant enzyme were similar to those of the wild type enzyme, but its substrate-dependent NADH oxidation activity in the presence of putidaredoxin (Pd) and putidaredoxin reductase (PdR) was extremely low. The rate constant of electron transfer from reduced Pd to the heme of the mutant P450cam, measured on an anaerobic stopped flow apparatus, was 1/400 of that of the wild type enzyme and the dissociation constant of the mutant P450cam for oxidized Pd was several fold higher than that of the wild type enzyme. A considerable decrease in mid-point potential of the mutant enzyme was also noted. We conclude that Arg112, which is located on the surface of the P450cam molecule and hydrogen-bonded to one of the heme propionate chains, plays an essential role in the electron transfer from Pd.

Arginine↗
PubMed1996

N-(2-ferrocene-ethyl)maleimide: a new electroactive sulphydryl-specific reagent for cysteine-containing peptides and proteins.

We report the synthesis and application of a specific electroactive label, N-(2-ferrocene-ethyl)maleimide, which provides new redox properties to organic compounds and proteins possessing sulphydryl groups. Its reaction conditions with the cysteine-containing peptide, glutathione, and a terminal monooxygenase enzyme, cytochrome P450cam are presented. The labelled peptide and enzyme acquired reversible electrochemical properties due to the attached ferrocene moiety.

Bacillus cereus↗
PubMed1992

Effects of 2-camphanone on canine portal vein blood flow and rat smooth muscle.

2-Camphanone is under clinical evaluation for alleviation of hemorrhoidal bleeding and inflammation. Reduced portal venous blood flow may distend, whereas improved portal venous blood flow may alleviate, hemorrhoidal vein distention. The effects of 2-camphanone on canine portal venous blood flow were investigated using pulsed Doppler flow techniques and on the spontaneous contractions of the isolated rat portal vein. Both intravenous (0.06, 0.2, and 0.6 mg/kg) and transdermal (6 mg/dog on the thigh) administration of 2-camphanone to dogs anesthetized with pentobarbital sodium increased portal venous flow velocity by 20%-30% without affecting femoral arterial blood flow, heart rate, or arterial blood pressure compared with vehicle-treated animals. Transdermal administration of 0.6, 2, and 6 mg of 2-camphanone, in a volume of 0.1 mL, to rats decreased the spontaneous contractions of the isolated rat portal vein in vitro. The data suggest that 2-camphanone exhibits a relatively selective effect on portal venous smooth muscle to reduce venous congestion and increase blood flow velocity. 2-Camphanone may be useful in the treatment not only of hemorrhoids, but also of esophageal reflux and portal hypertension.

Administration, Cutaneous↗
PubMed1994

Crystal structure and refinement of cytochrome P450terp at 2.3 A resolution.

Cytochrome P450terp is a class I (mitochondrial/bacterial) P450 that catalyzes the hydroxylation of alpha-terpineol as part of the catabolic assimilation of this compound by a pseudomonad species. Crystals grown from the purified protein have the symmetry of space group P6(1)22, and cell dimensions a = b = 69.4 A, c = 456.6 A, alpha = beta = 90 degrees, gamma = 120 degrees. Diffraction data were collected at the Cornell High Energy Synchrotron Source, and the structure of P450terp was solved by a combination of molecular replacement and multiple isomorphous replacement techniques. A model of P450terp was built and refined against native data, to an R-factor of 18.9% for data with I > or = sigma(I) between 6.0 A and 2.3 A resolution. This model contains 412 of the 428 P450terp amino acid residues; the loop between helices F and G is disordered in the crystal. While the overall fold of P450terp is very similar to that of P450cam, only three-quarters of the C alpha positions can be superimposed, to a root-mean-square deviation of only 1.87 A. The mode of substrate binding by P450terp can be predicted, and probable substrate contact residues identified. The heme environment and side-chain positions in the adjacent I-helix suggest possible modes of proton delivery in the catalytic cycle of the enzyme.

Amino Acid Sequence↗