Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0847097 (acidity)
 15,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The kinetic properties of sorbitol dehydrogenase from calf liver cell cytoplasm during sorbitol oxidation were studied at pH 7.0, 7.5, 8.0, 9.0 and 10.0. It was found that the shape of kinetic curves for NADH accumulation depends on pH and substrate concentration. At pH 7.0, 7.5 and 8.0 the enzymatic reaction obeys the Michaelis-Menten kinetics with Km of 3.3 x 10(-3) M. 2.3 x 10(-3) M and 2.08 x 10(-3) M, respectively. At pH 9.0 and 10.0 the vovs [So] curves have an "intermediate plateau". The Hill plots for this reaction reveal two slopes that are dependent on substrate concentration. The nH values for sorbitol (up to 2 mM) are 1.0 and 1.16 at pH 9.0 and 10.0, respectively. With a further rise in the substrate concentration, the nH value increases up to 2.4 and 2.18 at pH 9.0 and 10.0, respectively. This is suggestive of the existence of a slowly dissociating enzymatic system of the Np in equilibrium P type (where P is the oligomeric and p the monomeric forms of the enzyme); N approximately greater than 2. The vovs NAD plots are S-shaped at all pH values studied. The data obtained are discussed in terms of regulatory effects of sorbitol and acidity on association-dissociation of sorbitol dehydrogenase from liver cell cytoplasm.
 ...
PMID:[Kinetic properties of sorbitol dehydrogenase from calf liver cell cytoplasm]. 237 13

1. The reversible NAD(+)-linked oxidation of d-3-hydroxybutyrate to acetoacetate in 0.1m-sodium pyrophosphate buffer, pH8.5, at 25.0 degrees C, catalysed by d-3-hydroxybutyrate dehydrogenase (d-3-hydroxybutyrate-NAD(+) oxidoreductase, EC 1.1.1.30), was studied kinetically at chemical equilibrium by monitoring radioisotope redistribution with sodium dl-hydroxy[3-(14)C]butyrate and [4-(3)H]NAD(+)(labelled in the nicotinamide ring). 2. When all substrates are maintained at concentrations approaching saturation (approx. 3-50 times the K(m) values) the first-order rate constant for the enzyme-catalysed interconversion of NAD(+) and NADH is much smaller than that for the enzyme-catalysed interconversion of d-3-hydroxybutyrate and acetoacetate. 3. The rate of interconversion of NAD(+) and NADH increases initially with increasing concentrations of d-3-hydroxybutyrate and acetoacetate (ratio of concentrations maintained constant), passes through a maximum and approaches closely to zero at saturating concentrations of the latter substrates. 4. The rates of interconversion of NAD(+) and NADH and of d-3-hydroxybutyrate and acetoacetate increase with increasing concentration of NAD(+) (up to 66 times its K(m) value) and NADH (up to 180 times its K(m) value) (ratio of the concentrations of the nicotinamide nucleotides maintained constant). 5. These findings support the description of this catalysis as an ordered Bi Bi mechanism with no detectable alternative pathway, in which the interconversion of the central ternary complexes is not rate-limiting, and provide no evidence for the formation of dead-end complexes. 6. The solubility of 2,4-dinitrophenylhydrazine in HCl exhibits an acidity optimum, the maximum solubility at 25.0 degrees C (3.8mg/ml, 19mm) occurring at 2.29m-HCl; in solutions of this acidity acetone 2,4-dinitrophenylhydrazone is relatively insoluble (0.098mg/ml, 0.413mm).
 ...
PMID:D-3-hydroxybutyrate dehydrogenase from Rhodopseudomonas spheroides. Kinetics of radioisotope redistribution at chemical equilibrium catalysed by the enzyme in solutions. 435 36

Ultracytochemistry was used to study and compare cytochromooxidase, succinate dehydrogenase and NADH-dehydrogenase activity in gastric mucosa parietal cells in health and in gastric carcinoma associated with decreased acidity of gastric juice. The study demonstrated the reduced activity of the enzymes listed in the mucosal parietal cells in gastric carcinoma. This finding is interpreted as a consequence of disturbed energy supply of hydrochloric acid secretion in gastric carcinoma.
 ...
PMID:[Ultracytochemical study of oxidoreductases in the parietal cells of the gastric mucosa in gastric cancer]. 626 28

The synergism between coenzyme and anion binding to liver alcohol dehydrogenase has been examined by equilibrium measurements and transient-state kinetic methods to characterize electrostatic interactions of coenzymes with ligands which are bound to the catalytic zinc ion of the enzyme subunit. Inorganic anions typically exhibit an at least 200-fold higher affinity for the general anion-binding site than for catalytic zinc on complex formation with free enzyme. Acetate and SCN- interact more strongly with catalytic zinc in the enzyme X NAD+ complex than with the general anion-binding site in free enzyme. CN- shows no significant affinity for the general anion-binding site, but combines to catalytic zinc in the absence as well as the presence of coenzymes. Coordination of CN- to catalytic zinc weakens the binding of NADH by a factor of 50, and tightens the binding of NAD+ to approximately the same extent through interactions which do not include any contributions from covalent adduct formation between CN- and NAD+. These observations provide unambiguous information about the magnitude of electrostatic field effects of coenzymes on anion (e.g. hydroxyl ion) binding to catalytic zinc. They lead to the important inference that coenzyme binding must be strongly affected by ionization of zinc-bound water irrespective of the actual acidity of the latter group. It is concluded on such grounds that the much debated pH dependence of coenzyme binding to liver alcohol dehydrogenase must derive from ionization of zinc-bound water. The assumption that such is not the case leads to the inference that there is no detectable effect of ionization of zinc-bound water on coenzyme binding over the pH range 6-12, a possibility which is definitely excluded by the present results.
 ...
PMID:Electrostatic field effects of coenzymes on ligand binding to catalytic zinc in liver alcohol dehydrogenase. 636 76

Heterotropic cooperativity effects in the binding of alcohols and NAD+ or NADH to liver alcohol dehydrogenase have been examined by equilibrium measurements and stopped-flow kinetic studies. Equilibrium data are reported for benzyl alcohol, 2-chloroethanol, 2,2-dichloroethanol, and trifluoroethanol binding to free enzyme over the pH range 6-10. Binary-complex formation between enzyme and alcohols leads to inner-sphere coordination of the alcohol to catalytic zinc and shows a pH dependence reflecting the ionization states of zinc-bound water and the zinc-bound alcohol. The affinity of the binding protonation state of the enzyme for unionized alcohols increases approximately by a factor of 10 on complex formation between enzyme and NAD+ or NADH. The rate and kinetic cooperativity with coenzyme binding of the alcohol association step indicates that enzyme-bound alcohols participate in hydrogen bonding interactions which affect the rates of alcohol and coenzyme equilibration with the enzyme without providing any pronounced contribution to the net energetics of alcohol binding. The pKa values determined for alcohol deprotonation at the binary-complex level are linearly dependent on those of the free alcohols, and can be readily reconciled with the pKa values attributed to ionization of zinc-bound water. Alcohol coordination to catalytic zinc provides a major contribution to the pKa shift which ensures that the substrate is bound predominantly as an alcoholate ion in the catalytically productive ternary complex at physiological pH. The additional pKa shift contributed by NAD+ binding is less pronounced, but may be of particular mechanistic interest since it increases the acidity of zinc-bound alcohols relatively to that of zinc-bound water.
 ...
PMID:Synergism between coenzyme and alcohol binding to liver alcohol dehydrogenase. 638 67

The chain oxidation of glyceraldehyde-3-phosphate dehydrogenase.NADH by perhydroxyl radicals and propagated by molecular oxygen was studied by the xanthine-xanthine oxidase system, 60Co gamma-ray, and pulse radiolysis. The chain length, amount of NADH oxidized per HO2 generated, increases with increasing acidity of the medium and reaches a value of 73 at pH 5.0. The rate constant for the oxidation of the glyceraldehyde-3-phosphate dehydrogenase.NADH complex by HO2 was estimated to be 2 X 10(7) M-1 S-1 at ambient temperatures (23-24 degrees C). Rate studies as a function of pH indicate that O2- is unreactive toward the glyceraldehyde-3-phosphate dehydrogenase.NADH complex. Other dehydrogenases (malate dehydrogenase, glutamate dehydrogenase, and isocitric dehydrogenase) studied showed no catalytic activity in the oxidation of NADH by HO2/O2-.
 ...
PMID:Glyceraldehyde-3-phosphate dehydrogenase-catalyzed chain oxidation of reduced nicotinamide adenine dinucleotide by perhydroxyl radicals. 718 97

The survival and the physiology of lactococcal cells in the different compartments of the digestive tracts of rats were studied in order to know better the fate of ingested lactic acid bacteria after oral administration. For this purpose, we used strains marked with reporter genes, the luxA-luxB gene of Vibrio harveyi and the gfp gene of Aequora victoria, that allowed us to differentiate the inoculated bacteria from food and the other intestinal bacteria. Luciferase was chosen to measure the metabolic activity of Lactococcus lactis in the digestive tract because it requires NADH, which is available only in metabolically active cells. The green fluorescent protein was used to assess the bacterial lysis independently of death. We report not only that specific factors affect the cell viability and integrity in some digestive tract compartments but also that the way bacteria are administrated has a dramatic impact. Lactococci which transit with the diet are quite resistant to gastric acidity (90 to 98% survival). In contrast, only 10 to 30% of bacteria survive in the duodenum. Viable cells are metabolically active in each compartment of the digestive tract, whereas most dead cells appear to be subject to rapid lysis. This property suggests that lactococci could be used as a vector to deliver specifically into the duodenum the proteins produced in the cytoplasm. This type of delivery vector would be particularly appropriate for targeting digestive enzymes such as lipase to treat pancreatic deficiencies.
 ...
PMID:Survival, physiology, and lysis of Lactococcus lactis in the digestive tract. 1054 99

The phenol content and antioxidant activity of extra virgin olive oils (EVOOs) differing in their origins and degradation degrees were studied. The o-diphenolic compounds typical of olive oil, namely, the oleuropein derivatives hydroxytyrosol (3',4'-dihydroxyphenylethanol, 3',4'-DHPEA), the dialdehydic form of elenolic acid linked to 3',4'-DHPEA (3',4'-DHPEA-EDA), and an isomer of oleuropein aglycon (3',4'-DHPEA-EA), were analyzed by HPLC. The antioxidant activity was studied by (a) the xanthine oxidase (XOD)/xanthine system, which generates superoxide radical and hydrogen peroxide; (b) the diaphorase (DIA)/NADH/juglone system, which generates superoxide radical and semiquinonic radical; and (c) the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) test. Results showed that EVOOs with a low degradation level (as evaluated by acidity, peroxide number, and spectroscopic indices K(232), K(270), and deltaK according to the EU Regulation) had a higher content of 3',4'-DHPEA-EDA and a lower content of 3',4'-DHPEA than oils having intermediate and advanced degradation levels. EVOOs with a low degradation degree were 3-5 times more efficient as DPPH scavengers and 2 times more efficient as inhibitors of the XOD-catalyzed reaction than oils with intermediate and advanced degradation levels. The DIA-catalyzed reaction was inhibited by EVOOs having low or intermediate degradation levels but not by the most degraded oils.
 ...
PMID:Comparison of the antioxidant activities of extra virgin olive oils. 1247 92

The induction of CAM in Pedilanthus tithymaloides (Euphorbiaceae) under water-limited conditions was evaluated by following diurnal oscillations of CO2 fixation, titratable acidity and malic acid content in the leaf extracts. CAM induction was assessed by measuring the activities of phosphoenolpyruvate carboxylase (PEPC), NADH-malate dehydrogenase (MDH) and phosphoenolpyruvate caroxykinase (PEPCK) in the leaves as well. Drought resulted in large increases in the nocturnal acid accumulation and rates of CO2 uptake in the leaves of P. tithymaloides. The drought-induced CAM activity tended to be reversible after re-watering. Nevertheless, under well-watered conditions, plants of P. tithymaloides showed day time CO2 uptake patterns with less pronounced diurnal oscillations of organic acids. Our data indicate that although P. tithymaloides is a CAM plant, environmental variables like drought induce photosynthetic flexibility in this species. This type of plasticity in CAM and metabolic versatility in P. tithymaloides should be an adaptation for prolonged survival under natural adverse edaphic and microclimate situations.
 ...
PMID:Photosynthetic flexibility in Pedilanthus tithymaloides poit, a CAM plant. 1268 49

Two-electron oxidation of 2,2,5,7,8-pentamethyl-6-chromanol (PH), a model compound of alpha-tocopherol, gives the unstable 8a-hydroxy-2,2,5,7,8-pentamethyl-6-chromanone (POH) which rearranges to form stable 2-(3-hydroxy-3-methylbutyl)-3,5,6-trimethyl-1,4-benzoquinone (PQ). POH and PQ are isomers which have the same oxidation state. The aim of this work was to compare the ease of reduction of POH and PQ at room temperature using a variety of biological and chemical reductants in a reductant:POH (PQ) ratio of 20:1 (or 16:1). Ascorbic acid completely reduced POH to PH in 20 min, but had no effect on PQ after 40 min. Sodium ascorbate did not reduce POH or PQ at all after 40 min. Sodium dithionite reduced POH to PH (85%) in 20 min, but reduced PQ to its hydroquinone, PQH2 (67%) in 40 min. Dithiothreitol produced a slight reduction of POH to PH (21%) but reduced PQ to PQH2 (69%). NADH/FAD reduced POH and PQ to PQH2 (73% and 42%, respectively) in 10 min. It was concluded that POH is easier to reduce than PQ and more likely to form PH as a product, particularly under conditions of mild acidity.
 ...
PMID:Reduction of 8a-hydroxy-2,2,5,7,8-pentamethyl-6-chromanone. 1268 4


1 2 Next >>