Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: DrugBank:EXPT00568 (ascorbate)
 23,072 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. The properties of membrane vesicles from the extreme thermophile Bacillus caldolyticus were investigated. 2. Vesicles prepared by exposure of spheroplasts to ultrasound contained cytochromes a, b and c, and at 50 degrees C they rapidly oxidized NADH and ascorbate in the presence of tetramethyl-p-phenylenediamine. Succinate and l-malate were oxidized more slowly, and dl-lactate, l-alanine and glycerol 1-phosphate were not oxidized. 3. In the absence of proton-conducting uncouplers the oxidation of NADH was accompanied by a net translocation of H(+) into the vesicles. Hydrolysis of ATP by a dicyclohexylcarbodi-imide-sensitive adenosine triphosphatase was accompanied by a similarly directed net translocation of H(+). 4. Uncouplers (carbonyl cyanide p-trifluoromethoxyphenylhydrazone or valinomycin plus NH(4) (+)) prevented net H(+) translocation but stimulated ATP hydrolysis, NADH oxidation and ascorbate oxidation. The last result suggested an energy-conserving site in the respiratory chain between cytochrome c and oxygen. 5. Under anaerobic conditions the reduction of cytochrome b by ascorbate (with tetramethyl-p-phenylenediamine) was stimulated by ATP hydrolysis, indicating an energy-conserving site between cytochrome b and cytochrome c. However, no reduction of NAD(+) supported by oxidation of succinate, malate or ascorbate occurred, neither did it with these substrates in the presence of ATP under anaerobic conditions, suggesting that there was no energy-conserving site between NADH and cytochrome b. 6. Succinate oxidation, in contrast with that of NADH and ascorbate, was strongly inhibited by uncouplers and stimulated by ATP hydrolysis. These effects were not observed when phenazine methosulphate, which transfers electrons from succinate dehydrogenase directly to oxygen, was present. It was concluded that in these vesicles the oxidation of succinate was energy-dependent and that the reoxidation of reduced succinate dehydrogenase was dependent on the outward movement of H(+) by the protonmotive force. 7. In support of the foregoing conclusion it was shown that the reduction of fumarate by NADH was an energy-conserving process. 8. If the activities of vesicles accurately represent those of the intact organism it appears that in B. caldolyticus the reduction of fumarate to succinate at the expense of reducing equivalents from NADH is energetically favoured over succinate oxidation even under aerobic conditions. This may be related to the need for an ample supply of succinate for haem synthesis in order to provide cytochromes for the organism.
 ...
PMID:The oxidative activities of membrane vesicles from Bacillus caldolyticus. Energy-dependence of succinate oxidation. 20 11

1. The magnitude of the protonmotive force in respiring bovine heart submitochondrial particles was estimated. The membrane-potential component was determined from the uptake of S14CN-ions, and the pH-gradient component from the uptake of [14C]methylamine. In each case a flow-dialysis technique was used to monitor uptake. 2. With NADH as substrate the membrane potential was approx. 145mV and the pH gradient was between 0 and 0.5 unit when the particles were suspended in a Pi/Tris reaction medium. The addition of the permeant NO3-ion decreased the membrane potential with a corresponding increase in the pH gradient. In a medium containing 200mM-sucrose, 50mM-KCl and Hepes as buffer, the total protonmotive force was 185mV, comprising a membrane potential of 90mV and a pH gradient of 1.6 units. Thus the protonmotive force was slightly larger in the high-osmolarity medium. 3. The phosphorylation potential (= deltaG0' + RT ln[ATP]/[ADP][Pi]) was approx. 43.1 kJ/mol (10.3kcal/mol) in all the reaction media tested. Comparison of this value with the protonmotive force indicates that more than 2 and up to 3 protons must be moved across the membrane for each molecule of ATP synthesized by a chemiosmotic mechanism. 4. Succinate generated both a protonmotive force and a phosphorylation potential that were of similar magnitude to those observed with NADH as substrate. 5. Although oxidation of NADH supports a rate of ATP synthesis that is approximately twice that observed with succinate, respiration with either of these substrates generated a very similar protonmotive force. Thus there seemed to be no strict relation between the size of the protonmotive force and the phosphorylation rate. 6. In the presence of antimycin and/or 2-n-heptyl-4-hydroxyquinoline N-oxide, ascorbate oxidation with either NNN'N'-tetramethyl-p-phenylenediamine or 2,3,5,6-tetramethyl-p-phenylenediamine as electron mediator generated a membrane potential of approx. 90mV, but no pH gradient was detected, even in the presence of NO3-. These data are discussed with reference to the proposal that cytochrome oxidase contains a proton pump.
 ...
PMID:The protonmotive force in bovine heart submitochondrial particles. Magnitude, sites of generation and comparison with the phosphorylation potential. 21 21

1. The magnitude of the protonmotive force in phosphorylating membrane vesicles from Paracoccus denitrificans was estimated. The membrane potential component was determined from the uptake of S(14)CN(-), and the transmembrane pH gradient component from the uptake of [(14)C]methylamine. In each case a flow-dialysis technique was used to monitor uptake. 2. With NADH as substrate, the membrane potential was about 145mV and the pH gradient was below 0.5 pH unit. The membrane potential was decreased by approx. 15mV during ATP synthesis, and was abolished on addition of carbonyl cyanide p-trifluoromethoxyphenylhydrazone. In the presence of KCl plus valinomycin the membrane potential was replaced by a pH gradient of 1.5 units. 3. Succinate oxidation generated a membrane potential of approx. 125mV and the pH gradient was below 0.5 pH unit. Oxidation of ascorbate (in the presence of antimycin) with either 2,3,5,6-tetramethyl-p-phenylenediamine or NNN'N'-tetramethyl-p-phenylenediamine as electron mediator usually generated a membrane potential of approx. 90mV. On occasion, ascorbate oxidation did not generate a membrane potential, suggesting that the presence of a third energy-coupling site in P. denitrificans vesicles is variable. 4. With NADH or succinate as substrate, the phosphorylation potential (DeltaG(p)=DeltaG(0)'+RTln[ATP]/ [ADP][P(i)]) was approx. 53.6kJ/mol (12.8kcal/mol). Comparison of this value with the protonmotive force indicates that more than 3 protons need to be translocated via the adenosine triphosphatase of P. denitrificans for each molecule of ATP synthesized by a chemiosmotic mechanism. In the presence of 10mm-KNO(3) the protonmotive force was not detectable (<60mV) but DeltaG(p) was not altered. This result may indicate either that there is no relationship between the protonmotive force and DeltaG(p), or that for an unidentified reason the equilibration of SCN(-) or methylamine with the membrane potential and the pH gradient is prevented by NO(3) (-) in this system.
 ...
PMID:The protonmotive force in phosphorylating membrane vesicles from Paracoccus denitrificans. Magnitude, sites of generation and comparison with the phosphorylation potential. 21 22

A method is described for preparation of membrane vesicles (diameter 80nm) capable of respiration-linked ATP synthesis. Vesicles prepared from succinate-grown bacteria oxidized NADH, succinate and ascorbate plus NNN'N'-tetramethylphenylenediamine; vesicles prepared from methanol-grown bacteria also oxidized methanol and formaldehyde, but they were otherwise identical. The uncoupling agent carbonyl cyanide chlorophenylhydrazone and the adenosine triphosphatase inhibitor dicyclohexylcarbodi-imide both inhibited ATP synthesis, whereas they had no effect on the rate of respiration. Rotenone inhibited ATP synthesis and respiration with NADH as substrate; antimycin A inhibited with succinate as substrate, and cyanide inhibited with all substrates. P/O ratios were usually 0.7-1.3 with NADH, 0.6-1.0 with succinate and 0.2-0.6 with reduced NNN'N'-tetramethylphenylenediamine or methanol as respiratory substrate. When 2,6-dichlorophenol-indophenol was used as an alternative electron acceptor to O(2) (NADH as donor) the P/2e ratio was 1.65. Although these P/O ratios are minimum values, because they do not take into account unknown amounts of uncoupled O(2) consumption, they are consistent with previous proposals [O'Keeffe & Anthony (1978) Biochem, J.170, 561-567] based on measurements of proton translocation in whole cells. The results also confirm that methanol dehydrogenase and cytochromes c and a/a(3) are arranged so that the first step in methanol oxidation is coupled to synthesis of ATP.
 ...
PMID:The microbial metabolism of C1 compounds. Oxidative phosphorylation in membrane preparations of Pseudomonas AM1. 22 Sep 60

Crude preparations of kinetoplast vesicles were used to investigate the respiratory chain components in Leishmania tropica promastigotes. In difference spectra from enzymically and chemically reduced preparations, cytochrome b was the predominant component. By utilizing special assays designed to minimize the influence of cytochrome b on difference spectra, cytochromes a, a3 and c555 were demonstrated. Difference spectra from chemically reduced preparations indicated that pyridine nucleotides (NADH) and flavoproteins were also part of the respiratory chain. The presence of these components as well as their response to respiratory inhibitors and ascorbate provide evidence for the presence of a typical trypanosomatid respiratory chain in L. tropica promastigotes.
 ...
PMID:Respiratory chain components of Leishmania tropica promastigotes. 22 90

1. The uncoupler-stimulated ATPase activity of castor bean endosperm mitochondria and submitchondrial particles has been studied. The rate of ATP hydrolysis catalyzed by intact mitochondria was slow and little enhanced by addition of uncouplers at the concentration required for uncoupling the oxidative phosphorylation. ATP-ase activity was stimulated at higher concentrations of uncouplers. 2. 1-Anilinonaphthalene 8-sulfonate fluorescence was decreased when the mitochondria were oxidizing succinate. Carbonylcyanide-p-trifluoromethoxyphenylhydrazone and antimycin reversed the succinate-induced fluorescence diminution. ATP did not induce the fluorescence response. 3. The addition of succinate, NADH or ascorbate/N,N,N'-N'-tetramethyl-p-phenylenediamine as electron donor induced high ATPase activity in the presence of low concentrations of uncouplers. Stimulating effect of uncouplers was completely abolished by further addition of antimycin. 4. Submitochondrial particles were prepared by sonication. The particles catalyzed a rapid hydrolysis of ATP and carbonylcyanide-p-trifluoromethoxyphenylhydrazone at 10-8 M did not stimulate the ATPase activity. Addition of succinate induced uncoupler-stimulated ATPase activity. The effect of succinate was completely abolished by further addition of antimycin. 5. The treatment of submitochondrial particles by trypsin or high pH also induced uncoupler-stimulated ATPase activity. 6. The above results were interpreted to indicate that ATPase inhibitor regulated the back-flow reaction of mitochondrial oxidative phosphorylation.
 ...
PMID:Respiration-department uncoupler-stimulated ATPase activity in castor bean endosperm mitochondria and submitochondrial particles. 23 83

Ehrlich cells treated with dinitrophenol and iodoacetate rapidly recover their 30-sec uptake of 2-(methyl-amino)-isobutyrate on treatment with 0.1 mM phenazine methosulfate + 20 mM sodium ascorbate before they begin to recover from the severely depressed ATP levels and alkali-ion gradients. Addition of 10 mM pyruvate also restores uptake of methylaminoisobutyrate before the alkali-ion gradients rise. This restoration is prevented by rotenone, but rotenone does not handicap restoration by phenazine methosulfate/ascorbate. Na+-independent uptake of 2-aminonorbornane-2-carboxylate by Ehrlich cells is affected the same way. Quinacrine almost completely suppresses uptake of methylaminoisobutyrate within the 30-sec uptake test, even when ATP levels are sustained by pyruvate and alkali-ion gradients are not depressed. Ouabain prevents restoration of both Na+-dependent and Na+-independent amino-acid transport by phenazine methosulfate/ascorbate or pyruvate. We interpret these results to indicate that amino-acid transport can be energized not only by known means, but also by reducing equivalents, which presumably reach the plasma membrane in the form of NADH from the mitochondria when the source of energy is pyruvate. In support of this hypothesis, the distribution of methylaminoisobutyrate between plasma membrane vesicles and their supporting media was influenced in the predictable way by NADH, quinacrine, and an uncoupling agent, proceeding on the assumption that more of the vesicles had the everted rather than the natural orientation.
 ...
PMID:Unexpected additional mode of energization of amino-acid transport into Ehrlich cells. 26 89

The NADH oxidase activity of stage V mother-cell membranes, isolated from sporulating Bacillus megaterium KM, shows a greater inhibition by cyanide and displays this response at lower concentrations of cyanide than the stage V forespore inner membrane. Comparison of the effects of various respiratory inhibitors reveals that the difference in cyanide sensitivity between these membranes is located on the oxidase side of the 2-heptyl-4-hydroxyquinoline N-oxide-sensitive step. Both membranes contain cytochromes a+a3, b-562, b-555, c and d, with three potential oxidases: cytochromes a+a3, o and d. Cyanide difference spectra suggest that cytochromes b-562 and d may be the components involved in the cyanide-resistant electron transport pathway. Membrane ascorbate-N,N,N',N'-tetramethylphenylenediamine and ascorbate 2,6-dichlorophenolindophenol oxidase activities are highly sensitive to cyanide. Evidence is presented for terminal branching of the respiratory chain with branches differing in cyanide sensitivity. The cyanide sensitivity of the NADH oxidase of membranes prepared from various stages of sporulation is compared. Morphogenesis of the mother-cell plasma membrane to a cyanide-sensitive form during stages II and III of sporulation is postulated.
 ...
PMID:Cyanide-resistant electron transport in sporulating Bacillus megaterium KM. 40 13

When human red cells are incubated at 37 degrees C with the artificial electron donor system ascorbate + phenazine methosulphate the fluxes of Rb+ (K+) through the cell membrane are increased. The effect of this donor system is much stronger in energy-depleted than in normal cells. The same effects are produced by HS-glutathione, NADH or NADPH loaded into resealed ghosts, but these electron donors were ineffective when added to the incubation medium. The Rb+ (K+) fluxes induced by electron donors resemble closely those induced by an increase of intracellular Ca2+ (Gardos effect). The electron donors require the presence of intracellular Ca2+ to be effective, but at levels that do not stimulate by themselves the fluxes of K+. Flavoenzyme inhibitors (atebrin and chlorpromazine), oligomycin and quinine prevented the effects of both electron donors and Ca2+ alone; antimycin, upcouplers and ethacrynic acid inhibited them partially; ouabain, furosemide, and rotenone had no effect. The results could be explained if the effect of electron donors is to bring about a change in the redox state of some membrane component(s) that makes intracellular Ca2+ more effective to elicit rapid K+ movements. Plasma membrane oxidoreductase activities could be engaged in this change.
 ...
PMID:Stimulation of monovalent cation fluxes by electron donors in the human red cell membrane. 47 14

The influence of sodium nitroprusside (SNP) on mitochondrial respiration was examined in rat liver mitochondria. The addition of SNP 1 mmol litre-1 during state 3 respiration inhibited the oxygen uptake by 63.4%. A mixture of SNP 1 mmol litre-1 and glutathione (GSH) 1 mmol litre-1 inhibited the oxygen uptake more markedly (by 75.9%). The cyanide concentrations were 0.01 mmol litre-1 with SNP alone and 0.15 mmol litre-1 with the mixture of SNP and GSH. Cyanide production from SNP in the presence of various reducing agents was studied in potassium phosphate 0.1 mol litre-1 buffer solution (pH 7.4) incubated at 37 degrees C. Cyanide was liberated markedly from SNP in the presence of GSH or ascorbate. Less cyanide was produced in the presence of NADH or NADPH. The rate of production of cyanide was dependent entirely upon the concentration of each reducing agent added. No cyanide was liberated when sodium dithionite or the oxidized forms of GSH, NAD or NADP were used. It was concluded that SNP is degradated to cyanide by a hydrogen donor and that the cyanide liberated in this manner inhibits the cytochrome oxidase activity of mitochondria in vivo.
 ...
PMID:Inhibition of mitochondrial respiration by sodium nitroprusside and the mechanism of cyanide liberation. 58


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