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)

H+ titration curves of hen egg-white lysozyme were obtained at 0.15 I in the presence of small amounts (less than 15%) of methanol, ethanol and n-propanol. The acidity constants of two groups (whose pK values in water are, respectively, 42 and 3.5) are increased in water-alcohol mixtures in comparison to water. From the evaluation of these constants as a function of alcohol concentration and hydrocarbon chain length, it is suggested that these alcohols interact specifically with lysozyme. As pK values of 4.2 and 3.5 in water are generally assigned to Asp-101 and Asp-52 respectively, it seems that interaction occurs within the active site of the enzyme.
 ...
PMID:Hydrogen ion titration of lysozyme in alcohol-water solutions. 24 Apr 38

The rate constant for the catalytic transfer of the active-site PO3 group from rabbit muscle phosphoglucomutase to the hydroxyl group of a water molecule is about 3 x 10(-8) s-1 under optimal reaction conditions, but in the absence of the normal substrate, viz., at pH 7.5 and 30 degrees C, in the presence of saturating Mg2+; the corresponding constant for transfer to the 6-hydroxyl group of glucose 1-phosphate under analogous conditions, about 1000 s-1, is larger than this by some 3 x 10(10)-fold. Since no single factor appears to be capable of providing a rationale for a majority of this "substrate-induced rate effect" (Ray, jr., W.J., and Long, J.W. (1976), Biochemistry, the preceding paper in this issue), the change in the PO3-transfer rate produced by binding various parts of the phosphoglucosyl moiety to the enzyme, both separately and concurrently, was investigated. The rate of PO3 transfer to water is increased by up to 1000-fold by binding entities that provide the active site with a second PO3 group, e.g., ethyl phosphate or inorganic phosphite. Using an alcoholic acceptor further increases transfer efficiency (in the presence of bound phosphite): increase with methanol, about 2000-fold on a molar basis. The reactivities of ten other primary aliphatic alcohols vary by nearly 600-fold as the acidity of the PO3 acceptor is varied over a 4000-fold range. Although no straightforward relationship is observed between the efficiency of an alcohol as an acceptor and its acidity - presumably because of complications due to steric effects, for example - an increased transfer rate of 100-fold, relative to the water reaction, is estimated for a simple primary alcohol with a pKa similar to that expected for the 6-hydroxyl group of glucose 1-phosphate, when the alcohol is present at a concentration of 1 M. Joining an alcoholic acceptor and a PO3 group via five apparently inert bridging units changes PO3 transfer to an intramolecular process; in the case of 1,4-butanediol monophosphate the rate of transfer also increases by 240-fold, relative to the analogous reaction in the presence of 1 M propanol and bound inorganic phosphite. Comparable values also are obtained in comparisons of PO3 transfer rates for trans- 1,4-butenediol and 1,4-butynediol monophosphates relative to 1 M allyl and propargyl alcohols, respectively, in the presence of bound phosphite. An increased rate of transfer also is produced by binding the xylosyl part of the glucose ring, either when the acceptor is an hydroxyl group attached to the ring or when it is the hydroxyl group of a water molecule, e.g., as in the water reaction facilitated by bound xylose 1-phosphate. These and other results suggest that most of the differences between the rates of the water reaction and the glucose 1-phosphate reaction can be rationalized in terms of four fairly discrete factors whose approximate values are as follows: the PO4 factor, 1000-fold; the C-OH/H-OH factor, 100-fold; the nucleophile-binding factor, 250-fold; and the (CHOH)3-bridging factor, 200-fold...
 ...
PMID:An analysis of the substrate-induced rate effect in the phosphoglucomutase system. 96 19

The dependence of the ionic forms of haematoporphyrin(LX) dihydrochloride (HpdiCl) on solvent composition was investigated. In 2.8 x 10(-4) M solutions of HpdiCl in apolar (C6H6) and polar (CH3CN) solvents, HpdiCl exists in dicationic form. In hydrogen-bonding solvents, such as CH3OH, HpdiCl can exist in neutral, monocationic and dicationic forms. In C6H6-CH3OH solvent mixtures, the ionic forms in which HpdiCl is present depend on the composition of the solvent and on the acidity of the solution. The rate of oxidative photodegradation of HpdiCl excitation in its Q bands (WBI) and the ability to produce free radicals are different for the different ionic species. The highest values correspond to the dicationic form of HpdiCl and the lowest values correspond to the neutral species. In the absence of oxygen, the formation of free radicals due to the reaction of 3(Hp dication) is detected in the following solvent mixtures: CH3OH-toluene, CH3OH-ethylbenzene, CH3OH-hexane. The data obtained indicate that interaction of 3(Hp dication) with methine groups is an intermediate step in the formation of free radicals. In the HpdiCl concentration range studied, the presence of a phenolic antioxidant, such as beta-naphtol, inhibits the oxidative photodegradation of the dicationic form in a treated solution, but has little effect on the oxidative photobleaching of the monocation. The rate of oxidative photodegradation of the monocationic form increases with the addition of propionic acid to the solution.
 ...
PMID:Solvents effects in the photodegradation and reactivity of the various ionic forms of haematoporphyrin. 195 42

Prostaglandins, leukotrienes, and other metabolites of arachidonic acid can be conveniently and efficiently extracted from biological media using a precolumn containing octadecylsilyl silica connected to a 6-port switching valve that is in line with an analytical HPLC column. This procedure makes it possible to extract complex mixtures of eicosanoids and to analyze them by reversed-phase HPLC in a single step. The requirement to evaporate solvents from extracts prior to HPLC is therefore eliminated, saving time and reducing the possibilities for loss and contamination. The effects on recoveries of various media for loading the sample onto the precolumn were investigated, and it was concluded that 15% methanol at neutral pH gives the best overall results. It is therefore not necessary to acidity the sample prior to extraction, which simplifies the procedure and improves the recoveries of acid-labile eicosanoids. Following extraction, eicosanoids can be introduced onto the HPLC column by changing the position of the 6-port switching valve. We have investigated several approaches to the analysis of complex mixtures of these products by reversed-phase HPLC. The best results were obtained using a ternary gradient with a non-end-capped column of octadecylsilyl silica. Metabolites of arachidonic acid other than peptido-leukotrienes were first eluted by increasing the concentrations of acetonitrile and methanol in the mobile phase, which contained a constant concentration of trifluoroacetic acid (0.001%). Peptido-leukotrienes were then eluted with a second gradient, in which the concentrations of acetonitrile and methanol were kept constant, but the concentration of trifluoroacetic acid was increased to 0.0091%. Leukotrienes C4, D4, and E4 appear as sharp peaks at the end of the chromatogram and are completely separated from other types of arachidonic acid metabolites.
 ...
PMID:Precolumn extraction and reversed-phase high-pressure liquid chromatography of prostaglandins and leukotrienes. 282 29

1. Enrichment in the (S)-enantiomers for (R)-flurbiprofen, (R)-naproxen, (R)-suprofen and (R;S)-ibuprofen was investigated in various subcellular hepatic preparations containing coenzyme A. While such preparations were able to form hippuric acid from benzoic acid, the chiral inversion was never seen. 2. Using 2-dimethylaminoethanethiol 2-phenylpropionate (DEPP) as a model acyl thioester, the acidity of the methine proton was investigated by monitoring the proton/deuterium exchange occurring in deuterated solvents using high-resolution n.m.r. The compound was inert up to 22 h in D2O at 37 degrees C and pD 7.4. In pure methanol or a methanol-water mixture, only solvolysis was seen. In contrast, competitive hydrolysis (k = 0.005 h-1) and proton/deuterium exchange (k = 0.09 h-1) were seen in a CD3CN/D2O (50:50) mixture at 37 degrees C. 3. It is speculated that the failure to characterize chiral inversion of 2-arylpropionates in subcellular preparations may be due to the absence of a microenvironment of adequately moderate polarity.
 ...
PMID:Metabolic chiral inversion of anti-inflammatory 2-arylpropionates: lack of reaction in liver homogenates, and study of methine proton acidity. 284 Jul 82

The enzymatic reactions involving pyridoxal 5'-phosphate (PLP) can be simulated in solutions; thus, this system forms a favorable model for understanding the requirements of the enzymatic catalysis. We have studied in methanol protonic equilibria of the imines formed between PLP or salicylaldehyde (SA) and various amino acids, using UV and NMR spectroscopy. A glass electrode and an operational pH* scale were used to control acidity. The first protonation of the phosphate of PLP imines can be detected by UV spectroscopy with pK* at 10.8, proved by [31P]-NMR. The second protonation of phosphate (pK* at 4.8) is accompanied by increased hydrolysis of the imines. The imines of aspartate deviate from the imines of nondicarboxylic amino acids indicating that the beta-carboxyl of aspartate is internally hydrogen-bonded. PLP-2-aminobutanol Schiff base does not show with [1H]-NMR at pH* 7 separate peaks for ketoenamine-enolimine tautomers even at -90 degrees C, SA-phenylalanine shows an unidentified absorption at 350-380 nm. This was tentatively assigned a trans structure.
 ...
PMID:Acid-base chemistry of vitamin B6 compounds in methanol. 325 78

1. Steady-state kinetic parameters for the beta-galactosidase-catalysed hydrolysis of 13 aryl beta-d-galactopyranosides show no simple dependence on aglycone acidity. 2. alpha-Deuterium kinetic isotope effects (k(H)/k(D)) for seven of these substrates, measured under steady-state conditions with [S]>>K(m), vary from 1.00 for poor substrates to 1.25 for hydrolysis of the galactosyl-enzyme. 3. Methanolysis of the galactosyl-enzyme in 1.5m-methanol increases K(H)/k(D) for degalactosylation, but leaves that for hydrolysis of ;slow' substrates unchanged. 4. These data are incompatible with a simple two-step mechanism. A scheme consisting of a conformation change, liberation of a galactopyranosyl cation in an intimate ion-pair, non-productive but preferential collapse of the ion-pair to a covalent species and reaction of the galactosyl enzyme through the ion-paired form is proposed. 5. This scheme is used to rationalize previously puzzling data about the enzyme mechanism.
 ...
PMID:The mechanism of action of beta-galactosidase. Effect of aglycone nature and -deuterium substitution on the hydrolysis of aryl galactosides. 457 62

The present study demonstrated the cytoprotective abilities of low concentrations of ethanol, NaCl and HCl, against the gastric mucosal damage caused by 100% ethanol, and the contributions of the physical and chemical properties of these mild irritants to their protective actions. The results have shown the differential protective effects of ethanol (10-40%), NaCl (2.5-12.5%) and HCl (0.15-0.45M), with the optimal cytoprotective concentrations being 20% ethanol, 5% NaCl and 0.3M HCl, respectively. Solutions of KCl and NaCl with similar osmolarity, and H2SO4 and HCl of similar acidity and osmolarity, all showed similar protective protective potentials as compared to the osmotic agent mannitol, which possessed a concentration- and tonicity-dependent protective action against 100% ethanol-induced mucosal damage. Some concentration of methanol, propan-2-ol and ethanol, having similar osmolarity with deionized water, exerted indifferent protective effects. It is therefore concluded that adaptive cytoprotection induced by low concentrations of NaCl and HCl could depend on their physical properties, while that of ethanol could act through its unique chemical property.
 ...
PMID:Contributions of physical and chemical properties of mild irritants to gastric cytoprotection in rats. 759 13

Methyl angolensate (1), the major compound isolated from the methanol extract of the stem bark of Entandrophragma angolense produced a dose-related inhibition of gastric ulceration, 40 mg/kg body weight (B.W.) being more effective than 40 mg/kg B.W. of propranolol. The highest dose used (80 mg/kg B.W.) completely inhibited gastric ulceration and significantly reduced gastric acidity (P < 0.05). Furthermore, 1 (40 mg/kg B.W.) significantly reduced gastric acid secretion induced by histamine (1.0 mg/kg B.W.) and carbachol (1.0 mg/kg B.W.). These results suggest that 1 produces its antiulcer activity by inhibition of gastric acid secretion.
 ...
PMID:Methyl angolensate: the antiulcer agent of the stem bark of Entandrophragma angolense. 770 Oct 5

The application of pH-zone-refining counter-current chromatography (CCC) to the preparative separation of stereoisomeric acids is described. The separation was accomplished on the basis of the difference in acidity of the two stereoisomers. pH-Zone-refining CCC of 400 mg of a crude synthetic mixture of stereoisomeric 1-methyl-4-methoxymethylcyclohexanecarboxylic acids yielded 49.5 and 40 mg of the pure Z- and E-stereoisomers respectively. The two-phase solvent system consisted of hexane-ethyl acetate-methanol-water (1:1:1:1). Trifluoro acetic and octanoic acids were used as retainer acids. The eluent base was aqueous ammonia. The eluted fraction were monitored by gas chromatography-mass spectrometry.
 ...
PMID:Preparative separation of stereoisomeric 1-methyl-4-methoxymethylcyclohexanecarboxylic acids by pH-zone-refining counter-current chromatography. 784 45


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