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)

Membrane vesicles of Veillonella alcalescens, grown in the presence of L-lactate and KNO-3, actively transport amino acids under anaerobic conditions in the presence of several electron donors and the electron acceptor nitrate. The highest initial rates of uptake are obtained with L-lactate, followed by reduced nicotinamide adenine dinucleotide, glycerol-1-phosphate, formate, and L-malate.. The membrane vesicles contain the dehydrogenases for these electron donors, and these enzymes are coupled with nitrate reductase. In membrane vesicles from cells, grown in the presence of nitrate, the dehydrogenases are not coupled with fumarate reducatase, and anaerobic transport of amino acids does not occur with fumarate as electron acceptor. Under aerobic conditions none of the physiological electron donors can energize transport. However, a high rate of uptake is observed with the electron donor system ascorbate-phenazine metho-sulfate. This electron donor system also effectively energizes transport under anaerobicconditions in the presence of the electron acceptor nitrate.
 ...
PMID:Amino acid transport in membrane vesicles of obligately anaerobic Veillonella alcalescens. 16 33

It was possible to quantitate the tetramethyl-p-phenylenediamine (TMPD) oxidase reaction in Azotobacter vinelandii strain O using turbidimetrically standarized resting cell suspensions. The Q(O2) value obtained for whole cell oxidation of ascorbate-TMPD appeared to reflect the full measure of the high respiratory oxidative capability usually exhibited by this genera of organisms. The Q(O2) value for the TMPD oxidase reaction ranged from 1,700 to 2,000 and this value was equivalent to that obtained for the oxidation of the growth substrate, e.g., acetate. The kinetic analyses for TMPD oxidation by whole cells was similar to that obtained for the "particulate" A. vinelandii electron transport particle, that fraction which TMPD oxidase activity is exclusively associated with. Under the conditions used, there appeared to be no permeability problems; TMPD (reduced by ascorbate) readily penetrated the cell and oxidized at a rate comparable to that of the growth substrate. This, however, was not true for the oxidation of another electron donor, 2,6-dichloroindophenol, whose whole cell Q(O2) values, under comparable conditions, were twofold lower. The TMPD oxidase activity in A. vinelandii whole cells was found to be affected by the physiological growth conditions, and resting cells obtained from cells grown on sucrose, either under nitrogen-fixing conditions or on nitrate as the combined nitrogen source, exhibited low TMPD oxidase rates. Such low TMPD oxidase rates were also noted for chemically induced pleomorphic A. vinelandii cells, which suggests that modified growth conditions can (i) alter the nature of the intracellular terminal oxidase formed (or induced), or (ii) alter surface permeability, depending upon the growth conditions used. Preliminary studies on the quantitative TMPD oxidation reaction in mutant whole cells of both Azotobacter and a well-known Mucor bacilliformis strain AY1, deficient in cytochrome oxidase activity, showed this assay can be very useful for detecting respiratory deficiencies in the metabolism of whole cells.
 ...
PMID:Tetramethyl-p-phenylenediamine oxidase reaction in Azotobacter vinelandii. 17 91

The membrane-bound respiratory system of the gram-negative bacterium Spirillum itersonii was investigated. It contains cytochromes b (558), c (550), and o (558) and beta-dihydro-nicotinamide adenine dinucleotide (NADH) and succinate oxidase activities under all growth conditions. It is also capable of producing D-lactate and alpha-glycerophosphate dehydrogenases when grown with lactate or glycerol as sole carbon source. Membrane-bound malate dehydrogenase was not detectable under any conditions, although there is high activity of soluble nicotinamide adenine dinucleotide: malate dehydrogenase. When grown with oxygen as the sole terminal electron acceptor, approximately 60% of the total b-type cytochrome is present as cytochrome o, whereas only 40% is present as cytochrome o in cells grown with nitrate in the presence of oxygen. Both NADH and succinate oxidase are inhibited by azide, cyanide, antimycin A, and 2-n-heptyl-4-hydroxyquinoline-N-oxidase at low concentrations. The ability of these inhibitors to completely inhibit oxidase activity at low concentrations and their effects upon the aerobic steady-state reduction levels of b- and c-type cytochromes as well as the aerobic steady-state reduction levels obtained with NADH, succinate, and ascorbate-dichlorophenolindophenol suggest that presence of an unbranched respiratory chain in S. itersonii with the order ubiquinone leads to b leads to c leads to c leads to oxygen.
 ...
PMID:Membrane-bound respiratory of Spirillum itersonii. 18 74

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

Trinitroglycerin oxidizes the essential sulfhydryl group, Cys-149, of pig muscle glyceraldehyde-3-phosphate dehydrogenase (D-glyceraldehyde-3-phosphate : NAD+ oxidoreductase(phosphorylating) EC 1.2.1.12) TO A SLUFENIC ACID, NOT TO A DISULFIDE. This conclusion is based on the observation that the inactivation of the dehydrogenase activity of the enzyme by the organic nitrate induces the acylphosphatase activity which is catalyzed by the sulfenic acid form of the enzyme. Inorganic nitrite is released during this process which is stoichiometric with the degree of inactivation of the dehydrogenase. The acylphosphatase activity induced by trinitroglycerin, unlike the dehydrogenase activity, is sensitive to CN-. Treatment of the enzyme oxidized with trinitroglycerin with 14-CN- leads to the incorporation of protein-bound 14-CN-, which is stoichiometric with the degree of inactivation of the dehydrogenase. Treatment of the sulfenic acid form of glyceraldehyde-3-phosphate dehydrogenase at pH 5.3 with a 10-fold molar excess of azide over the concentration of enzyme subunit completely inactivates the acylphosphatase reaction catalyzed by the oxidized enzyme. Concomitantly, the dehydrogenase activity catalyzed by the sulfhydryl form of the enzyme reappears which indicates that excess azide reduces the sulfenic acid which is required for the acylphosphatase. Treatment of the oxidized enzyme with a stoichiometric amount of azide at pH 5.3 stimulates the acylphosphatase activity and does not lead to the reappearance of dehydrogenase activity. When the sulfenic acid form of the enzyme is incubated with 20 mM L-ascorbate at pH 5.3, the acylphosphatase activity is completely inactivated and the dehydrogenase activity catalyzed by the reduced form of the enzyme is recovered. Thus, L-ascorbate also reduces the protein sulfenic acid which is required for the acylphosphatase activity.
 ...
PMID:The conversion of glyceraldehyde-3-phosphate dehydrogenase to an acylphosphatase by trinitroglycerin and inactivation of this activity by azide and ascorbate. 23 96

Gastrointestinal cancers, mainly oesophageal, gastric, pancreatic and large bowel cancer, account for about 40,000 deaths annually in England and Wales which is 32% of all cancer deaths. Nutritional factors have been implicated in the cause of each cancer and probably act by promoting the effect of carcinogenic substances taken in the diet or produced in the gut. Gastric cancer for example may be due to nitrosamine production in the stomach. This is enhanced by readily available sources of dietary nitrite and nitrate whilst the reaction is inhibited by vitamin C and low temperatures (2 degrees C). By contrast large bowel cancer can be related to high fat and meat intakes whilst a protective role for dietary fibre has been suggested. Dietary factors in the aetiology of oesophageal cancer differ from one high incidence area to another.
 ...
PMID:Dietary factors in the aetiology of gastrointestinal cancer. 36 21

Nutrients as therapy for patients with cancer are important as adjunctive therapy, i.e., adequate nutrition may be important for the success of whatever form of therapy is administered. Diets deficient in certain amino acids have some selectivity when tested against experimental tumors propagated in vivo. Such diets have had limited clinical trial and have been characterized by poor patient acceptance. Enzymes that produce deficiencies of certain amino acids, e.g., asparaginase, glutaminase, methioninase appear to offer a more reasonable approach to development of selective amino acid deficiencies in man. Trace metals in excessive amounts may be toxic or carcinogenic to the host. Two heavy metal salts, Cis-diamine dichloroplatinum and gallium nitrate, have recently been shown to have anti-neoplastic effects in man. There is no conclusive evidence that vitamins, administered in large doses, have significant antineoplastic effects although large doses of vitamin A, vitamin C, and vitamin B12 have been used for this purpose. In contrast, certain vitamin analogs such as folate antimetabolites can cause tumor regression and are useful clinical treatment. An enzyme, carboxypeptidase G1, by splitting naturally occurring folates, may also have promise as a method of producing enzymic folate deficiency.
 ...
PMID:Nutrients, vitamins and minerals as therapy. 37 10

Active transport of amino acids by membrane vesicles from Escherichia coli, grown anaerobically on glucose in the presence of nitrate, can be energized under anaerobic conditions by electron transfer in the nitrate respiration system with formate as electron donor and nitrate as acceptor. A high rate of amino acid transport is also obtained under anaerobic conditions by electron transfer from formate to the nitrate analogue chlorate or to the membrane-impermeable electron acceptor ferricyanide. Electron transfer from formate to nitrate results in the generation of an electrical potential as is indicated by the uptake of the lipophilic cation triphenylmethylphosphonium. Ferricyanide accpets electrons from at least two sites of the nitrate respiration system. One of these sites appears to be nitrate reductase, because cytochrome b, reduced by formate, is completely reoxidized by ferricyanide and glutamate transport energized by formate plus ferricyanide and formate plus nitrate are affected by the same electron transfer inhibitors. A second site of electron transfer to ferricyanide appears to be located prior to nitrate reductase in the nitrate respiration system, since formate is oxidized at a higher rate in the presence of ferricyanide than with nitrate while formate/ferricyanide energizes transport of amino acids at a lower rate than formate/nitrate. Moreover, electron transfer inhibitors block electron transfer from formate to nitrate to a significantly higher extent than from formate to ferricyanide. The effects of irradiation of the membrane vesicles with near ultra-violet light suggest that quinones play an essential role in the electron transfer from formate to nitrate or ferricyanide. Irradiation blocks completely formate-dependent nitrate and ferricyanide reduction and active transport driven by formate/nitrate and formate/ferricyanide, but has hardly any effect on the activity of formate dehydrogenase and on ascorbate/phenazine methosulphate/oxygen-driven transport. Similar effects of ferricyanide have been observed in membrane vesicles from E. coli, grown anaerobically in the presence of fumarate. In these membrane vesicles a high rate of lactose and triphenylmethylphosphonium uptake under anaerobic conditions is obtained by electron transfer from glycerol 1-phosphate to fumarate and also to ferricyanide and evidence has been presented for the involvement of cytochromes in these electron transfers.
 ...
PMID:Active transport by membrane vesicles from anaerobically grown Escherichia coli energized by electron transfer to ferricyanide and chlorate. 79 48

Nitrosamines are an extremely carcinogenic class of compounds. The hasard, bound with the occurrence of this compounds in the food and the possibility to be formed in vivo, during the digestion, justifies the current works. The authors quoting numerous works on different laboratory's animals, remind the toxicity. and carcinogenicity of this compounds. The metabolism is also discussed. The N-nitroso, compounds may be formed in food from the presence of the precursors (nitrite or nitrate, amines and amino-acides). The synthesis takes place during the technological processes, the storage and the house cooking. Today, the marginal effect dose is estimated as 10 mug/kg of daily food. The carcinogenicity has not been demonstrated in human, but is strongly suspected. The amount of N-nitroso compounds in human food is generally low. Many factors can influence the reaction; it is inversely related to the basicity of secondary amine and optimum pH is around pH 4. A lot of compounds such as sodium ascorbate inhibit the synthesis in food. A number of recent reports using reliable methodology have identified nitrosamines at the lower part per billion level. Dimethyl-nitrosamines occurs, very sporadically in a number of cooked meat samples. The nitrosopyrrolidine appears frequently in fried but not in uncooked products. The nitrosopiperidine seems to be bind with the presence of pepper in food. Finally the presence of nitrosamides (nitrososarcosine) and nitrosoaminoacides (nitrosoproline, nitrosohydroxy-proline) is being quested. The N-nitroso compounds may be synthetized in vivo during the digestion at the acide medium of the stomach or by bacterial action during the transit in the gut...
 ...
PMID:[Nitrosamines. Review]. 101 37

The formation of nitrite from nitrate was studied in potatoes incubated at room temperature. After 24 hours of incubation at 25 degrees, 112 ppm and 373 ppm of nitrite formed in homogenized cooked potatoes containing 284 ppm and 584 ppm of nitrate, respectively. In homogenized fresh potatoes incubated at 21 degrees and containing 284 ppm of nitrate, 103 ppm of nitrate formed within 24 hours. During the period of nitrite formation, nitrate levels decreased sharply, indicating that reduction of nitrate to nitrite occurred. Incubation at 2 degrees completely prevented nitrite formation in all cases. The formation of methylnitrosourea from added methylurea and nitrite was observed in potato incubated under simulated gastric conditions (37 degrees, pH 1.5). An ascorbate-nitrite mole ratio of 4 gave a 93% inhibition of methylnitrosourea formation. Ascorbate reacted directly with nitrite in potato incubated under identical conditions, yielding a 43% decrease in nitrite concentration. Ascorbate did not react with methylurea or the product, methylnitrosourea.
 ...
PMID:Reduction of gastric carcinogens with ascorbic acid. 106 Apr 1


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