scholarly journals The effects of halothane on hepatic microsomal electron transfer

1975 ◽  
Vol 148 (2) ◽  
pp. 179-186 ◽  
Author(s):  
M C Berman ◽  
K M Ivanetich ◽  
J E Kench
Keyword(s):  
Electron Transfer ◽  
Desaturase Activity ◽  
Anaesthetic Agent ◽  
Reductase Activity ◽  
Electron Flow ◽  
Cytochrome B5 ◽  
Order Rate Constant ◽  
Redox Equilibrium ◽  
Microsomal Cytochrome B5 ◽  
Nadh Cytochrome

1. The effects of halothane (CF3CHBrCl), a volatile anaesthetic agent, on electron transfer in isolated rat liver microsomal preparations were examined. 2. At halothane concentrations achieved in tissues during clinical anaesthesia (1-2mM), halothane shifts the redox equilibrium of microsomal cytochrome b5 in the presence of NADPH towards the oxidized form. Halothane accelerates stoicheiometric consumption of NADPH and O2, increases the rate of reoxidation of NADH-reduced microsomal ferrocytochrom b5, but does not affect NADPH- or NADH-cytochrome c reductase activity. The enhanced microsomal electron flow seen in the presence of halothane is not diminished by CO nor is it increased by pretreatment of the animals with phenobarbital. 3. The effects of halothane are maximum in microsomal preparations isolated from animals fed on a high-carbohydrate diet to induce stearate desaturase activity. Changes in microsomal electron transfer caused by halothane are in all cases abolished by low concentrations (1-2mM) of cyanide. Microsomal stearate desaturase activity is unaffected by halothane. 4. The first-order rate constant for oxidation of membrane-bound ferrocytochrome b5 in the absence of added substrate (k1 equals 1.5 times 10(-3)A-1) is similar to that for autoxidation of purified ferrocytochrome b5(k1 equals 7 times 10(-3)S-1) the rate of autoxidation of soluble ferrocytochrome b5 is unaffected by halothane. 5. It is concluded that the effects of halothane on microsomal electron transfer are not related to cytochrome P-450 linked metabolism but rather arise from the interaction of halothane with the cyanide-sensitive factor of the stearate desaturase pathway.

scholarly journals Molecular and antigenic properties of cytochrome b5 from slow-muscle sarcoplasmic reticulum

1981 ◽  
Vol 197 (2) ◽  
pp. 515-518 ◽  
Author(s):  
G Salviati ◽  
S Salvatori ◽  
R Betto ◽  
A Margreth
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Reductase Activity ◽  
Polyacrylamide Gel Electrophoresis ◽  
Cytochrome B5 ◽  
Slow Muscle ◽  
Molecular Weights ◽  
Antigenic Properties ◽  
Microsomal Cytochrome B5 ◽  
Membrane Bound ◽  
Nadh Cytochrome

NADH-cytochrome b5 reductase and cytochrome b5 associated with slow-muscle sarcoplasmic reticulum and liver microsomal fraction were identified with discrete protein bands of molecular weights 33000 and 16700 by polyacrylamide-gel electrophoresis. Purified detergent-extracted cytochrome b5 from muscle sarcoplasmic reticulum is indistinguishable from liver microsomal cytochrome b5 with respect to spectral properties, pI values and immunological reactivity with antibody to the liver cytochrome b5. Reaction of the antibody with membrane-bound cytochrome b5 inhibits the sarcoplasmic-reticulum NADH-cytochrome c reductase activity.

scholarly journals NADPH: cytochrome P-450 reductase in olfactory epithelium Relevance to cytochrome P-450-dependent reactions

1986 ◽  
Vol 240 (2) ◽  
pp. 585-592 ◽  
Author(s):  
C J Reed ◽  
E A Lock ◽  
F De Matteis
Keyword(s):  
Olfactory Epithelium ◽  
Direct Evidence ◽  
Reductase Activity ◽  
Electron Flow ◽  
Male Rats ◽  
Male And Female ◽  
Marked Activity ◽  
Nadh Cytochrome ◽  
Olfactory Tissue ◽  
Cytochrome P 450

The presence of a very active cytochrome P-450-dependent drug-metabolizing system in the olfactory epithelium has been confirmed by using 7-ethoxycoumarin, 7-ethoxyresorufin, hexobarbitone and aniline as substrates, and the reasons for the marked activity of the cytochrome P-450 in this tissue have been investigated. The spectral interaction of hexobarbitone and aniline with hepatic and olfactory microsomes has been examined. By this criterion there was no evidence for marked differences in the spin state of the cytochromes of the two tissues, or for the olfactory epithelium containing a greater amount of cytochrome capable of binding hexobarbitone, a very actively metabolized substrate. Rates of NADPH and NADH: cytochrome c reductase activity were found to be higher in the olfactory epithelium than in the liver, and direct evidence was obtained for a greater amount of the NADPH-dependent flavoprotein in the olfactory microsomes. Investigation of male rats and male and female mice, as well as male hamsters, demonstrated that, in all cases, the cytochrome P-450 levels of the olfactory epithelium were lower than those of the liver, while the 7-ethoxycoumarin de-ethylase and NADPH:cytochrome c reductase activities were higher. A correlation was found between 7-ethoxycoumarin de-ethylase and NADPH:cytochrome c reductase activities for both tissues in all species examined. The ratio of reductase to cytochrome P-450 was found to be considerably higher in the olfactory epithelium (1:2-1:3) than in the liver (1:11-1:15), regardless of the species examined, suggesting that facilitated electron flow may contribute significantly to the cytochrome P-450 catalytic turnover in the olfactory tissue.

Phenobarbital-induced increase of NADH-cytochrome b5 reductase activity in rat liver microsonies

1978 ◽  
Vol 27 (3) ◽  
pp. 367-368 ◽  
Author(s):  
Ademar Vieira De Barros ◽  
Jean-Claude Kaplan ◽  
Philippe Duvaldestin ◽  
Pierre Berthelot
Keyword(s):  
Rat Liver ◽  
Reductase Activity ◽  
Cytochrome B5 ◽  
Cytochrome B5 Reductase ◽  
Nadh Cytochrome

scholarly journals Autoxidation of soluble trypsin-cleaved microsomal ferrocytochrome b5 and formation of superoxide radicals

1976 ◽  
Vol 157 (1) ◽  
pp. 237-246 ◽  
Author(s):  
M C Berman ◽  
C M Adnams ◽  
K M Ivanetich ◽  
J E Kench
Keyword(s):  
Superoxide Dismutase ◽  
Rate Constant ◽  
Phosphate Buffer ◽  
Electron Flow ◽  
Cytochrome B5 ◽  
Significant Proportion ◽  
Intrinsic Property ◽  
Order Rate Constant ◽  
Rapid Phase ◽  
Autoxidation Reaction

The rate and mechanism of autoxidation of soluble ferrocytochrome b5, prepared from liver microsomal suspensions, appear to reflect an intrinsic property of membrane-bound cytochrome b5. The first-order rate constant for autoxidation of trypsin-cleaved ferrocytochrome b5, prepared by reduction with dithionite, was 2.00 × 10(−3) +/− 0.19 × 10(−3) S-1 (mean +/− S.E.M., n =8) when measured at 30 degrees C in 10 mM-phosphate buffer, pH 7.4. At 37 degrees C in aerated 10 mM-phosphate buffer (pH 7.4)/0.15 M-KCl, the rate constant was 5.6 × 10(-3) S-1. The autoxidation reaction was faster at lower pH values and at high ionic strengths. Unlike ferromyoglobin, the autoxidation reaction of which is maximal at low O2 concentrations, autoxidation of ferrocytochrome b5 showed a simple O2-dependence with an apparent Km for O2 of 2.28 × 10(-4) M (approx. 20kPa or 150mmHg)9 During autoxidation, 0.25 mol of O2 was consumed per mol of cytochrome oxidized. Cyanide, nucleophilic anions, EDTA and catalase each had little or no effect on autoxidation rates. Adrenaline significantly enhanced autoxidation rates, causing a tenfold increase at 0.6 mM. Ferrocytochrome b5 reduced an excess of cytochrome c in a biphasic manner. An initial rapid phase, independent of O2 concentration, was unaffected by superoxide dismutase. A subsequent slower phase, which continued for up to 60 min, was retarded at low O2 concentrations and inhibited by 65% by superoxide dismutase at a concentration of 3 mug/ml. It is concluded that autoxidation is responsible for a significant proportion of electron flow between cytochrome b5 and O2 in liver endoplasmic membranes, this reaction being capable of generating superoxide anions. A biological role for the reaction is discussed.

scholarly journals Minireview: Regulation of Steroidogenesis by Electron Transfer

Endocrinology ◽  
2005 ◽  
Vol 146 (6) ◽  
pp. 2544-2550 ◽  
Author(s):  
Walter L. Miller
Keyword(s):  
Electron Transfer ◽  
Electron Flow ◽  
Cytochrome B5 ◽  
Serine Phosphorylation ◽  
Molar Ratio ◽  
Type I ◽  
Type Ii ◽  
Cytochrome P450 Enzymes ◽  
Redox Partners ◽  
P450 Enzyme

Abstract Cytochrome P450 enzymes catalyze the degradation of drugs and xenobiotics, but also catalyze a wide variety of biosynthetic processes, including most steps in steroidogenesis. The catalytic rate of a P450 enzyme is determined in large part by the rate of electron transfer from its redox partners. Type I P450 enzymes, found in mitochondria, receive electrons from reduced nicotinamide adenine dinucleotide (NADPH) via the intermediacy of two proteins—ferredoxin reductase (a flavoprotein) and ferredoxin (an iron/sulfur protein). Type I P450 enzymes include the cholesterol side-chain cleavage enzyme (P450scc), the two isozymes of 11-hydroxylase (P450c11β and P450c11AS), and several vitamin D-metabolizing enzymes. Disorders of these enzymes, but not of the two redox partners, have been described. Type II P450 enzymes, found in the endoplasmic reticulum, receive electrons from NADPH via P450 oxidoreductase (POR), which contains two flavin moieties. Steroidogenic Type II P450 enzymes include 17α-hydroxylase/17,20 lyase (P450c17), 21-hydroxylase (P450c21), and aromatase (P450aro). All P450 enzymes catalyze multiple reactions, but P450c17 appears to be unique in that the ratio of its activities is regulated at a posttranslational level. Three factors can increase the degree of 17,20 lyase activity relative to the 17α-hydroxylase activity by increasing electron flow from POR: a high molar ratio of POR to P450c17, serine phosphorylation of P450c17, and the presence of cytochrome b5, acting as an allosteric factor to promote the interaction of POR with P450c17. POR is required for the activity of all 50 human Type II P450 enzymes, and ablation of the Por gene in mice causes embryonic lethality. Nevertheless, mutation of the human POR gene is compatible with life, causing multiple steroidogenic defects and a skeletal dysplasia called Antley-Bixler syndrome.

scholarly journals PGR5 is required for efficient Q cycle in the cytochrome b6f complex during cyclic electron flow

2019 ◽  
Author(s):  
Felix Buchert ◽  
Laura Mosebach ◽  
Philipp Gäbelein ◽  
Michael Hippler
Keyword(s):  
Electron Transfer ◽  
Reductase Activity ◽  
Electron Flow ◽  
Cyclic Electron Flow ◽  
Redox Activity ◽  
Q Cycle ◽  
Redox Tuning ◽  
Photosynthetic Control ◽  
Photosynthetic Electron Transfer

AbstractProton Gradient Regulation 5 (PGR5) is involved in the control of photosynthetic electron transfer but its mechanistic role is not yet clear. Several models have been proposed to explain phenotypes such as a diminished steady state proton motive force (pmf) and increased photodamage of photosystem I (PSI). Playing a regulatory role in cyclic electron flow (CEF) around PSI, PGR5 contributes indirectly to PSI protection by enhancing photosynthetic control, which is a pH-dependent downregulation of electron transfer at the cytochrome b6f complex (b6f). Here, we re-evaluated the role of PGR5 in the green alga Chlamydomonas reinhardtii and conclude that pgr5 possesses a dysfunctional b6f. Our data indicate that the b6f low-potential chain redox activity likely operated in two distinct modes – via the canonical Q cycle during linear electron flow and via an alternative Q cycle during CEF, attributing a ferredoxin-plastoquinone reductase activity to the b6f. The latter mode allowed efficient oxidation of the low-potential chain in the WT b6f. A switch between the two Q cycle modes was dependent of PGR5 and relied on unknown stromal electron carrier(s), which were a general requirement for b6f activity. In CEF-favouring conditions the electron transfer bottleneck in pgr5 was the b6f and insufficient flexibility in the low-potential chain redox tuning might account for the mutant pmf phenotype and the secondary consequences. Models of our findings are discussed.

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