AUTOTROPHIC ENZYME SYSTEMS: I. ELECTRON TRANSPORT SYSTEMS CONCERNED WITH HYDROXYLAMINE OXIDATION IN NITROSOMONAS

1963 ◽  
Vol 41 (1) ◽  
pp. 763-778 ◽  
Author(s):  
M. I. H. Aleem ◽  
H. Lees
Keyword(s):  
Electron Transport ◽  
Cytochrome C ◽  
Ammonium Ion ◽  
Transport Systems ◽  
Enzyme Complex ◽  
Reaction Sequence ◽  
Intact Cells ◽  
Cytochrome C Reductase ◽  
Enzyme Systems ◽  
Low Concentrations

Intact cells or cell-free extracts of Nitrosomonas catalyze the rapid and stoichiometric conversion of nitrohydroxylamine to nitrite at rates comparable to the oxidation of ammonium ion or hydroxylamine to nitrite. Cell-free extracts possess a powerful hydroxylamine – cytochrome c reductase activating hydroxylamine to donate electrons to the cytochrome systems comprising b, c, and a type components. The partially purified enzyme complex is sensitive to low concentrations of cyanide and inhibitors of the flavoproteins. The possible mechanism of the formation and oxidation of the new intermediate "nitrohydroxylamine" in the reaction sequence is discussed.

AUTOTROPHIC ENZYME SYSTEMS: I. ELECTRON TRANSPORT SYSTEMS CONCERNED WITH HYDROXYLAMINE OXIDATION IN NITROSOMONAS

1963 ◽  
Vol 41 (3) ◽  
pp. 763-778 ◽  
Author(s):  
M. I. H. Aleem ◽  
H. Lees
Keyword(s):  
Electron Transport ◽  
Cytochrome C ◽  
Ammonium Ion ◽  
Transport Systems ◽  
Enzyme Complex ◽  
Reaction Sequence ◽  
Intact Cells ◽  
Cytochrome C Reductase ◽  
Enzyme Systems ◽  
Low Concentrations

Intact cells or cell-free extracts of Nitrosomonas catalyze the rapid and stoichiometric conversion of nitrohydroxylamine to nitrite at rates comparable to the oxidation of ammonium ion or hydroxylamine to nitrite. Cell-free extracts possess a powerful hydroxylamine – cytochrome c reductase activating hydroxylamine to donate electrons to the cytochrome systems comprising b, c, and a type components. The partially purified enzyme complex is sensitive to low concentrations of cyanide and inhibitors of the flavoproteins. The possible mechanism of the formation and oxidation of the new intermediate "nitrohydroxylamine" in the reaction sequence is discussed.

Comparative studies on succinate and terminal oxidase activity in microbial and mammalian electron-transport systems

1969 ◽  
Vol 15 (7) ◽  
pp. 797-807 ◽  
Author(s):  
Peter Jurtshuk ◽  
Ann K. May ◽  
Leodocia M. Pope ◽  
Patricia R. Aston
Keyword(s):  
Electron Transport ◽  
Cytochrome C ◽  
Comparative Studies ◽  
Azotobacter Vinelandii ◽  
Transport Systems ◽  
Terminal Oxidase ◽  
Succinate Oxidation ◽  
State Reduction ◽  
Hydroxy Quinoline ◽  
Terminal Oxidation

A comparative study was undertaken to examine the succinate and terminal oxidase activities of the electron-transport systems of Azotobacter vinelandii and mammalian mitochondria. For succinate oxidation, both systems exhibited similar relative specificities for the electron acceptors phenazine methosulfate, O2, methylene blue, K3Fe(CN)6, nitrotetrazolium blue, 2,6-dichlorophenolindophenol (DCIP), and cytochrome c. They differed in that DCIP and cytochrome c were less active in the Azotobacter electron-transport system (R3 fraction) than in the bovine mitochondrial system. Comparative studies with known inhibitors of mammalian mitochondrial electron-transport demonstrated that the succinoxidase activity of the Azotobacter R3 fraction was, at least, 2000 times less sensitive to antimycin A, 700 times less sensitive to thenoyl-trifluoroacetone, and 30 times less sensitive to 2-n-heptyl-4-hydroxy-quinoline-N-oxide. Both systems were equally sensitive to KCN, p-chloromercuribenzoic acid, and chlorpromazine.The ability of the two systems to use tetramethyl-p-phenylenediamine (TMPD) and its derivatives as electron donors, for terminal oxidation, was also similar. Studies on steady state reduction revealed that in the Azotobacter R3 fraction, the cytochromes (a2, a1, b1, c4 + c5) and flavoprotein components were reduced substantially by succinate as well as by TMPD in the presence of ascorbate. Ultrastructure analyses of the Azotobacter R3 electron-transport fraction revealed the vesicular membranous components identified as oxidosomes according to the terminology used by DeLey and contained spherical headpiece units of 80 Å in diameter which appeared to be morphologically identical with the tripartite units or the elementary particles described by Green and associates, viz., Kopaczyk et al., and by Fernandez-Moran et al.

Electron Transport and Coupled Energy Generation in Pseudomonas saccharophila

1971 ◽  
Vol 49 (11) ◽  
pp. 1175-1182 ◽  
Author(s):  
M. Ishaque ◽  
A. Donawa ◽  
M. I. H. Aleem
Keyword(s):  
Oxygen Consumption ◽  
Electron Transport ◽  
Cytochrome C ◽  
Atp Synthesis ◽  
Succinate Oxidation ◽  
Atp Formation ◽  
Low Concentrations ◽  
Oxidase Enzyme ◽  
Succinate Oxidase ◽  
Pseudomonas Saccharophila

The respiratory chain system of heterotrophically grown Pseudomonas saccharophila contained cytochromes of the b, c, a, and o types and also the NADH and succinate oxidase enzyme systems. Cell-free extracts catalyzed phosphorylation coupled to the oxidation of NADH, succinate, and ascorbate (plus cytochrome c). The P/O ratios were in the range of 1.00 for generated NADH, 0.29 for added NADH, 0.50 for succinate, and 0.25 for ascorbate (plus cytochrome c).The oxidative phosphorylation was uncoupled by 2,4-dinitrophenol, 2,6-dibromophenol, pentachlorophenol, m-chlorocarbonyl cyanide phenylhydrazone, and dicumarol without any inhibition of oxygen consumption. Phosphorylation coupled to NADH oxidation was completely inhibited by the flavoprotein inhibitors such as rotenone, amytal, and atabrine; these inhibitors had no effect, however, on the ATP synthesis associated with succinate oxidation. Antimycin A or 2-n-nonyl-4-hydroxyquinoline-N-oxide as well as cyanide or azide at low concentrations completely inhibited the phosphate esterification coupled to the oxidation of NADH or succinate, but had little or no effect on the oxygen consumption. Relatively higher concentrations of oligomycin were required for a complete inhibition of the electron-transport-linked ATP formation.

Acute inhibition of respiratory capacity of muscle reduces peak oxygen consumption

1990 ◽  
Vol 259 (6) ◽  
pp. C889-C896 ◽  
Author(s):  
R. M. McAllister ◽  
R. L. Terjung
Keyword(s):  
Oxygen Consumption ◽  
Electron Transport ◽  
Cytochrome C ◽  
Peak Oxygen Consumption ◽  
Dependent Manner ◽  
Cytochrome C Reductase ◽  
Energy Demands ◽  
Hindlimb Muscle ◽  
Nadh Cytochrome

Electron transport capacity of skeletal muscle was inhibited in situ in an acute dose-dependent manner with myxothiazol, a tight-binding inhibitor of ubiquinone-cytochrome c reductase, complex III of the respiratory chain. Peak oxygen consumption of rat hindlimb muscle was determined via consecutive 10-min isometric contraction (100 ms at 100 Hz) periods of increasing energy demands (4, 8, 15, 30, 45, and 60 tetani/min), using an isolated hindlimb preparation perfused with a high oxygen delivery (approximately 6-8 mumol.min-1.g-1). Peak oxygen consumption decreased from 4.61 +/- 0.19 mumol.min-1.g-1 (control) in a dose-dependent manner to 0.73 +/- 0.07 mumol.min-1.g-1 at 0.50 microM myxothiazol in blood. Oxygen extraction decreased from 65 to 12% of delivered oxygen. Furthermore, the reduction in peak respiratory rate became evident at lower energy demands of the contraction sequence. Myxothiazol inhibition of respiration was not dependent on the presence of muscle contractions but was evident when mitochondria were uncoupled with carbonyl cyanide m-chlorophenylhydrazone. A 50% effective dosage (ED50) of 0.21 microM myxothiazol for inhibition of peak oxygen consumption closely resembled the inhibition of NADH-cytochrome c reductase activity (ED50 of 0.27 microM) determined from homogenates of the same muscles. This suggests that the peak oxygen consumption of skeletal muscle is tightly coupled to the capacity for electron transport evaluated by flux through NADH-cytochrome c reductase. If the enzyme activity measured in vitro correctly represents available enzymatic capacity within contracting muscle, approximately 75% of electron transport capacity for handling reducing equivalents generated from NADH is utilized during peak oxygen consumption of rat hindlimb muscle contracting in situ.

scholarly journals Dimethylnitrosamine demethylation by reconstituted liver microsomal cytochrome P-450 enzyme system

1975 ◽  
Vol 152 (3) ◽  
pp. 705-708 ◽  
Author(s):  
P D Lotlikar ◽  
W J Baldy ◽  
E N Dwyer
Keyword(s):  
Cytochrome C ◽  
Enzyme System ◽  
Microsomal Cytochrome ◽  
Cytochrome C Reductase ◽  
Oxidative Demethylation ◽  
Enzyme Systems ◽  
Triton X ◽  
Cytochrome P 450 ◽  
Nadph Cytochrome C Reductase ◽  
Demethylation Activity

Oxidative demethylation of dimethylnitosamine was studied with both reconstituted and unresolved liver microsomal cytochrome P-450 enzyme systems from rats and hamsters. Proteinase treatment of liver microsomal preparations yielded cytochrome P-450 particulate fractions. Both cytochrome P-450 and NADPH- cytochrome c reductase fractions were required for optimum demethylation activity. Particulate cytochrome P-450 fractions were more effecient than either Triton X-100- or cholatesolubilized preparations of these particles in demethylation activity with rat and hamster liver preparations appear to be due to differences in specificity in their cytochrome P-450 fractions.

scholarly journals Structural and functional relationships of enzyme activities induced by nitrate in barley

1970 ◽  
Vol 119 (4) ◽  
pp. 715-725 ◽  
Author(s):  
John L. Wray ◽  
Philip Filner
Keyword(s):  
Cytochrome C ◽  
Nitrate Reductase ◽  
Nitrate Reductase Activity ◽  
Reductase Activity ◽  
Bottom Layer ◽  
Sucrose Density Gradient ◽  
Enzyme Complex ◽  
Cytochrome C Reductase ◽  
Functional Relationships ◽  
Nadh Cytochrome

1. Nitrate induces the development of NADH-nitrate reductase (EC 1.6.6.1), FMNH2–nitrate reductase and NADH–cytochrome c reductase activities in barley shoots. 2. Sucrose-density-gradient analysis shows one band of NADH–nitrate reductase (8S), one band of FMNH2–nitrate reductase activity (8S) and three bands of NADH–cytochrome c reductase activity (bottom layer, 8S and 3.7S). Both 8S and 3.7S NADH–cytochrome c reductase activities are inducible by nitrate, but the induction of the 8S band is much more marked. 3. The 8S NADH–cytochrome c reductase band co-sediments with both NADH–nitrate reductase activity and FMNH2–nitrate reductase activity. Nitrite reductase activity (4.6S) did not coincide with the activity of either the 8S or the 3.7S NADH–cytochrome c reductase. 4. FMNH2–nitrate reductase activity is more stable (t½ 12.5min) than either NADH–nitrate reductase activity (t½ 0.5min) or total NADH–cytochrome c reductase activity (t½ 1.5min) at 45°C. 5. NADH–cytochrome c reductase and NADH–nitrate reductase activities are more sensitive to p-chloromercuribenzoate than is FMNH2–nitrate reductase activity. 6. Tungstate prevents the formation of NADH–nitrate reductase and FMNH2–nitrate reductase activities, but it causes superinduction of NADH–cytochrome c reductase activity. Molybdate overcomes the effects of tungstate. 7. The same three bands (bottom layer, 8S and 3.7S) of NADH–cytochrome c reductase activity are observed irrespective of whether induction is carried out in the presence or absence of tungstate, but only the activities in the 8S and 3.7S bands are increased. 8. The results support the idea that NADH–nitrate reductase, FMNH2–nitrate reductase and NADH–cytochrome c reductase are activities of the same enzyme complex, and that in the presence of tungstate the 8S enzyme complex is formed but is functional only with respect to NADH–cytochrome c reductase activity.

Increased peak oxygen consumption of trained muscle requires increased electron flux capacity

1994 ◽  
Vol 77 (4) ◽  
pp. 1941-1952 ◽  
Author(s):  
D. M. Robinson ◽  
R. W. Ogilvie ◽  
P. C. Tullson ◽  
R. L. Terjung
Keyword(s):  
Electron Transport ◽  
Cytochrome C ◽  
Reductase Activity ◽  
Tight Binding ◽  
Treadmill Running ◽  
Complex Iii ◽  
Peak Oxygen Consumption ◽  
Transport Capacity ◽  
Cytochrome C Reductase ◽  
Nadh Cytochrome

The importance of the training-induced increase in mitochondrial capacity in realizing the increase in maximal O2 consumption (VO2max) of trained muscle was evaluated using an isolated perfused rat hindlimb preparation at a high blood flow (approximately 80 ml.min-1.100 g-1) during tetanic contractions. Rats trained for 8-–12 wk by treadmill running exhibited an approximately 25% increase in muscle VO2max (5.62 +/- 0.31 to 7.06 +/- 0.64 mumol.min-1.g-1), an increase in mitochondrial enzyme activity (approximately 70% for cytochrome oxidase and approximately 55% for NADH cytochrome-c reductase), and an increase in tissue capillarity (14%) that is expected to increase the O2 exchange capacity of the tissue. Muscle VO2max of sedentary (n = 34) and trained (n = 30) animals was determined, and electron transport capacity was acutely managed with myxothiazol, a tight-binding inhibitor of complex III. Inhibition of complex III was similar among 1) the low- and high-oxidative fibers and 2) the superficial and deep mitochondrial populations within muscle. Inhibition of NADH cytochrome-c reductase activity resulted in reductions in muscle VO2max with similar dose responses (mean effective dose of approximately 0.2 microM) of myxothiazol added to the perfusion medium. The extraction of O2 by the contracting muscle decreased as VO2max declined. The increase in muscle VO2max observed in the muscle of trained animals was eliminated when its electron transport capacity was reduced to that observed in normal sedentary rat muscle. Thus, the exercise-induced adaptation of an increased muscle mitochondrial content appears to be essential for trained muscle to exhibit its increased O2 flux capacity. The results of the present experiment illustrate the importance of mitochondrial adaptations in muscle remodeled by exercise training.

Immunochemical studies utilizing antibody to NADPH-cytochrome c reductase as a specific inhibitor of microsomal electron transport

1971 ◽  
Vol 3 (4) ◽  
pp. 296-299 ◽  
Author(s):  
Bettie Sue S. Masters ◽  
Edward B. Nelson ◽  
Daniel M. Ziegler ◽  
Jeffrey Baron ◽  
P. Prithvi Raj ◽  
...  
Keyword(s):  
Electron Transport ◽  
Cytochrome C ◽  
Specific Inhibitor ◽  
Cytochrome C Reductase ◽  
Nadph Cytochrome ◽  
Nadph Cytochrome C Reductase
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