Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.6.99.3 (diaphorase)
 5,903 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

During early postnatal development there was an increase in the specific activity of a number of oxidative enzymes localized on the outer and inner mitochondrial membrane. The succinic oxidase complex of the inner mitochondrial membrane, whose activity in 1-day-old rats was 50% of the value in adult animals, attained the maximum on about the 10th day after birth. Activity of the choline and the proline oxidase complex, both of which are also localized in the inner mitochondrial membrane, was minimal in 1-day-old rats and went on rising after the 10th day. Rotenone-insensitive NADH-cytochrome c reductase activity, which is localized on the outer mitochondrial membrane, remained stable up to the 10th day, and rose between the 10th and the 90th day. Developmental changes in monoaminooxidase activity, which is likewise localized on the outer mitochondrial membrane, followed a similar course to the choline and proline oxidase complexes. The amount of cytochromes a+alpha3 and cytochrome b in isolated mitochondria did not alter during development. The protein spectrum of the mitochondrial particles, determined by polyacrylamide gel electrophoresis in sodium dodecyl sulphate, likewise displayed no marked changes during postnatal development. The above findings show that the metabolic functions of the mitochondria mature during development and that changes in the different enzymes have their own characteristic time course.
 ...
PMID:The development of oxidative enzymes in rat liver mitochondria. 14 72

1. Respiration of chemotrophically and phototrophically grown Rhodospirillum rubrum is inhibited by 2-hydroxydiphenyl. 2. Membrane-bound NADH oxidase and NADH: cytochrome c reductase are inhibited also. The inhibitor constant for both reactions (Ki) is 0.075 plus or minus 0.012 mM. NADH dehydrogenase is not inhibited significantly. 3. The inhibition of succinate:cytochrome c reductase is associated for chemotrophic membranes with Ki equals 0.22 plus or minus 0.03 mM and for phototrophic membranes with Ki equals 0.49 plus or minus 0.09 mM. Succinate dehydrogenase is not affected by 2-hydroxydiphenyl. 4. Cytochrome oxidase is inhibited only slightly. 5. While NADH-dependent reactions in both phototrophic and chemotrophic membranes are inhibited maximally more than 95 percent, succinate-dependent reactions can be inhibited more than 95 percent only in chemotrophic membranes. In phototrophic membranes the maximum inhibition of succinate-dependent reactions is about 70 percent. 6. The type of inhibition in both cases 2 and 3 is non-competitive. 7. While the reduction of b-type cytochrome is inhibited by 2-hydroxydiphenyl, the degree of ubiquinone reduction is not influenced. The data suggest that the site of inhibition is localized between ubiquinone and cytochrome b. 8. Implications of these data for the respiratory electron transport system in R. rubrum are discussed.
 ...
PMID:Separation of respiratory reactions in Rhodospirillum rubrum: inhibition studies with 2-hydroxydiphenyl. 16 37

1. Electron transport particles obtained from cell-free extracts of Propionibacterium shermanii by centrifugation at 105000 times g for 3 hrs oxidized NADH, D,L-lactate, L-glycerol-3-phosphate and succinate with oxygen and, except for succinate, with fumarate, too. 2. Spectral investigation of the electron transport particles revealed the presence of cytochromes b, d and o, and traces of cytochrome alpha1 and a c-type cytochrome. Cytochrome b was reduced by succinate to about 50%, and by NADH, lactate or glycerol-3-phosphate to 80--90%. 3. The inhibitory effects of amytal and rotenone on NADH oxidation, but not on the oxidation of the other substrates, indicated the presence of the NADH dehydrogenase complex, or "site I region", in the electron transport system of P. shermanii. 4. NQNO inhibited substrate oxidations by oxygen and fumarate, as well as equilibration of the flavoproteins of the substrate dehydrogenases by way of menaquinone. The inhibition occurred at low concentrations of the inhibitor and reached 80--100%, depending on the substrate tested. The site of inhibition of the respiratory activity was located between menaquinone and cytochrome b. In addition, inhibition of flavoprotein equilibration suggested that NQNO acted upon the electron transfer directed from menaquinol towards the acceptor to be reduced, either cytochrome b or the flavoproteins, which would include fumarate reductase. 5. In NQNO-inhibited particles, cytochrome b was not oxidized by oxygen-free fumarate, but readily oxidized by oxygen. It was concluded from this and the above evidence that the branching-point of the electron transport chain towards fumarate reductase was located at the menaquinone in P. shermanii. It was further concluded that all cytochromes were situated in the oxygen-linked branch of the chain, which formed a dead end of the system under anaerobic conditions. 6. Antimycin A inhibited only oxygen-linked reactions of the particles to about 50% at high concentrations of the inhibitor. Inhibitors of terminal oxidases were inactive, except for carbon monoxide.
 ...
PMID:The electron transport system of the anaerobic Propionibacterium shermanii: cytochrome and inhibitor studies. 16 27

When purified bovine cytochrome c1 is digested with trypsin under controlled conditions, the heme polypeptide is preferentially converted from a species of molecular weight 30,600 to a heme polypeptide of molecular weight 29,000. The trypsin sensitive peptide bond is located in the N-terminal region of the cytochrome. Both the reduced and oxidized cytochrome are susceptible to hydrolysis by trypsin at the same locus, but the reduced cytochrome is cleaved at an initial rate approximately twofold greater than the oxidized cytochrome. Membranous cytochrome c1, as occurring in cytochrome b-c1 complex or succinate-cytochrome c reductase complex, is not susceptible to trypsin proteolysis under similar conditions, nor after more extensive treatment of the membranes with trypsin, in spite of the fact that cytochrome c1 presumably comes into contact with cytochrome c at the membrane surface during electron transport. These findings are consistent with a model for the structure of cytochrome c1 in situ in which the cytochrome is an integral membrane protein, located primarily in the membrane continuum, while still having the heme-containing portion of the protein available at the membrane surface for electron transfer to cytochrome c.
 ...
PMID:Controlled digestion with trypsin as a structural probe for the N-terminal peptide of soluble and membranous cytochrome c. 16 81

Various respiratory electron transport activities of Rhodopseudomonas capsulata were studied in membrane fragments prepared from photosynthetically grown cells of a parental strain and two terminal oxidase-defective mutant strains. The NADH and succinate oxidase activities of the mutant having a functional N,N,N1,N1-tetramethyl-p-phenylenediamine oxidase, M6, were consideraly more sensitive to inhibition by either antimycin A or cyanide than the corresponding activities of the mutant lacking a functional N,N,N1,N1-tetramethyl-p-phenylenediamine oxidase, M7. The parental strain, Z-1, but not the mutants, showed biphasic inhibitory responses of NADH and succinate oxidase activities with either antimycin A or cyanide. In certain reactions no differences in inhibitor susceptibility were found among the strains tested, implying that the pathways involved were unaffected in the mutants. In this category were the actions of rotenone on NADH oxidase, antimycin A on cytochrome c reductase and, in M6 and Z-1, cyanide on N,N,N'N'-tetramethyl-p-phenylenediamine oxidase. These results suggest that the respiratory chain of the parental strain branches at the ubiquinone-cytochrome b region into two pathways, each branch goes to a distinct terminal oxidase, and either may be blocked independently by genetic mutation.
 ...
PMID:The branched respiratory system of photosynthetically grown Rhodopseudomonas capsulata. 17 46

Two distinct ferredosin-type iron-sulfur centers (designated as Centers S-1 and S-2) are present in the soulble succinate dehydrogenase in approximately equivalent concentrations to that of bound flavin. Both Centers S-1 and S-2 exhibit electron paramagnetic resonance absorbance in the reduced state at the same magnetic field (gz = 2.03, gy = 1.93, and gx = 1.91) with similar line shape. Center S-2 is reducible only chemically with dithionite and remains oxidized under physiological conditions. Thus, its functional role is unknown; however, thermodynamic and EPR characterization of this iron-sulfur center has revealed important molecular events related to this dehydrogenase. The midpoint potentials of Centers S-1 and S-2 determined in the soluble succinate dehydrogenase preparations are -5 +/- 15 mV and -400 +/- 15 mV, respectively, while corresponding midpoint potentials determined in particulate preparations, such as succinate-cytochrome c reductase or succinate-ubiquinone reductase, are 0 +/- 15 mV and -260 +/- 15 mV. Reconstitution of soluble succinate dehydrogenase with the cytochrome b-c1 complex is accompanied by a reversion of the Center S-I midpoint from -400 +/- 15 mV to -250 +/- 15 mV with a concomitant restoration of antimycin A-sensitive succinate-cytochrome c reductase activity. There observations indicate that, during the reconstitution process, Center S-I is restored to its original molecular environment. In the reconstitutively active succinate dehydrogenase, the relaxation time of Center S-2 is much shorter than that of S-1, thus Center S-2 spectra are well discernible only below 20 K (at 1 milliwatt of power), while the resonance absorbance of Center S-1 is detectable at higher temperatures and readily saturates below 15 K. Over a wide temperature range the power saturation of Center S-1 resonance absorbance is relieved by Center S-2 in the paramagnetic state, and the Center S-2 central resonance absorbance is broadened by Center S-1 spins, due to a spin-spin interaction between these centers. These observations indicate an adjacent location of these centers in the enzyme molecule. In reconstitutively inactive enzymes, subtle modification of the enzyme structure appears to shift the temperature dependence of Center S-2 relaxation to the higher temperature. Thus the EPR signals of Center S-2 are also detectable at higher temperature. In this system a splitting of the central peak of the Center S-2 spectrum due to spin-spin interaction was observed at extremely low temperatures, while this was not observed in reconstitutively active enzymes or in paritculate preparations. This spin-spin interaction phenomena of inactive enzymes disappeared upon chemical reactivation with concomitant appearance of the reconstitutive activity. These observations provide a close correlation between the molecular integrity of the enzyme and its physiological function.
 ...
PMID:Thermodynamic and EPR characteristics of two ferredoxin-type iron-sulfur centers in the succinate-ubiquinone reductase segment of the respiratory chain. 17 55

Puried complex III ) ubiquinol-cytochrome c reductase) from beef heart mitochondria was alkylated with iodol [1-14C]acetamide. After 6-8 h of incubation with iodo[1-14C]acetamide, duroquinol and ubiquinol-2-cytochrome c reductase activites were inhibited approximately 50%. During this time 4.5 +/- 1.6 nmol of iodo[1-14C]acetamide reacted per mg of complex III protein. Experiments carried out over 24 h indicated that enzyme activity could be inhibited to 70% and the alkylation of complex III was proportional to inhibition. The rates of cytochrome b and c1 reduction by duroquinol are also decreased upon treatment of complex III with iodoacetamide. Separation of the peptides of complex III by electrophoresis in sodium dodecylsulfate shows that all of the radioactivity is located in a single peptide of 50 000 molecular weight, which has been identified as one of the two core proteins. The possible functions of core protein are discussed.
 ...
PMID:Evidence for a function of core protein in complex III from beef-heart mitochondria. 18 53

The antibiotic funiculosin mimics the action of antimycin in several ways. It inhibits the oxidation of NADH and succinate, but not TMPD+ascorbate. The titer for maximal inhibition in Mg2+-ATP particles (0.4-0.6 nmol/mg protein) is close to the concentrations of cytochromes b and cc1. Funiculosin also induces the oxidation of cytochromes cc1 and an extra reduction of cytochrome b in the aerobic steady state, and it inhibits duroquinol-cytochrome c reductase activity in isolated Complex III. The location of the funiculosin binding site is clearly similar to that of antimycin. In addition, funiculosin, like antimycin, prevents electron transport from duroquinol to cytochrome b in isolated Complex III if the complex is pre-reduced with ascorbate. Funiculosin and antimycin differ, however, in the manner in which they modulate the reduction of cytochrome b by ascorbate+TMPD.
 ...
PMID:Funiculosin: an antibiotic with antimycin-like inhibitory properties. 19 85

The reduction of cytochrome c by the reduced form of the 6-decyl analogue of coenzyme Q follows first-order kinetics with respect to cytochrome c and increases in a linear manner with added mitochondrial protein. The activity is completely sensitive to antimycin A in whole cell extracts of yeast as well as in isolated mitochondria and fractionates with markers for the mitochondrial electron-transport chain. The presence of both cytochrome b and c1 in an approximately 2:1 ratio appears essential for enzymatic activity. Reduced coenzyme Q-cytochrome c reductase obeys Michaelis-Menten kinetics when assayed in mitochondria obtained from a yeast strain lacking coenzyme Q. Both reduced nitotinamide adenine dinucleotide and succinate:cytochrome c reductase activities were not detectable in six coenzyme Q deficient strains tested, but were restored after addition of the oxidized form of the coenzyme Q analogue. No marked difference in the concentration of the analogue required to restore the two activities was observed.
 ...
PMID:Role of coenzyme Q in the mitochondrial respiratory chain. Reconstitution of activity in coenzyme Q deficient mutants of yeast. 19 36

1) An isolation and purification procedure is reported for an active cytochrome b-c1 complex from Saccharomyces cerevisiae. The complex acts as an antimycin A-sensitive duroquinone-cytochrome c reductase and contains cytochromes b and c1 at a concentration of 8 nmol/mg protein and non-heme iron at a concentration of 15 nmol/mg protein. 2) Difference spectra at room temperature and at 70 degrees K show that the preparation is free from contamination with cytochromes c or aa3. Assays of enzyme activity indicate the absence of any of the other catalytic functions normally associated with the mitochondrial respiratory chain. 3) On dissociation and separation on sodium dodecylsulfate-polyacrylamide gels the complex gives rise to seven bands corresponding to subunit polypeptide molecular weights of 43 000, 40 000, 32 000, 24 000, 22 000, 20 000 and 18 000. These appear in a regular stoichiometry of 1:1:3:1:1:1:1.
 ...
PMID:Structure of a cytochrome b-c 1 complex from Saccharomyces cerevisiae YF. 20 May 45


1 2 3 4 5 6 7 8 9 10 Next >>