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Query: UMLS:C0847097 (acidity)
 15,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Linolenic acid (C18:3) is the main endogenous unsaturated fatty acid of thylakoid membrane lipids, and seems in its free form to exert significant effects on the structure and function of photosynthetic membranes. In this investigation the effect of linolenic acid was studied at various pH values on the electron flow rate in isolated spinach chloroplasts and related to deltapH, the proton pump and the pH of the inner thylakoid space (pHi). The deltapH and pHi were estimated from the extent of the fluorescence quenching of 9-aminoacridine. Linolenic acid caused a shift (approximately one unit) of the pH optimum for electron flow toward acidity in the following systems: (a) photosystems II + I (from H2O to NADP+ or to 2,6-dichlorophenolindophenol) coupled or non-coupled; (b) photosystem II (from H2O to 2,6-dichlorophenolindophenol in the presence of dibromothymoquinone). In photosystem I conditions (phenazine methosulphate), the deltapH of the control increased as a function of external pHo with a maximum around pH 8.8. When linolenic acid was added, the deltapH dropped, but its optimum was shifted toward more acidic pHo. The same phenomena were also observed in photosytems II + I (from H2O to ferricyanide) and in photosystem II conditions (from H2O to ferricyanide in the presence of dibromothymoquinone). However, the deltapH was smaller and the sensitivity of the proton gradient toward linolenic acid was eventually higher than for photosystem I electron flow activity. The proton pump which might be considered as a measure of the internal buffering capacity of thylakoids was optimum at pHo, 6.7 in the controls. An addition of linolenic acid diminished the proton pump and shifted its optimum toward higher pHo. As a consequence, pHi increased when pHo was raised. At the optimal pHo 8.6 to 9, pHi were 5 to 5.5. Additions of increasing concentrations of linolenic acid displaced the curves toward higher pHi. A decrease of pHo was therefore required to maintain the pHi in the range of 5-5.5 for maximum electron flow. In conclusion, the electron flow activity seems to be delicately controlled by the proton pump (buffer capacity), deltapH, pHi and pHo. Fatty acids damage the membrane integrity in such a way that the subtile equilibrium between the factors is disturbed.
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PMID:Influence of unsaturated fatty acids in chloroplasts. Shift of the pH optimum of electron flow and relations to deltapH, thylakoid internal pH and proton uptake. 0 70

Influence of pH on absorbance and CD-spectra of DNA in PEG-containing water-salt solutions has been studied. The changes in the spectra appeared due to disturbance of the DNA secondary structure upon acidification of the medium proir to or after DNA compactization. If acidification preceeds DNA compactization an intense negative band in the CD spectrum inherent to the compact particles is observed at pH values 7-4. The intensity of the band decreases with an increase of the acidity. The size of the compact particles as evaluated from the dependence of the apparent optical density on the wavelength value remains unchanged (about 1200 A). If the solution is strongly acidified (pH 4.0-2.8) and a considerable disturbance in the DNA secondary structure takes place a negative band in the CD spectrum completely disappears. If one acidifies a solution containing preformed DNA compact particles a decrease of the intensity of the CD negative band starts at lower pH values (less than 2.8). This process is accompanied by an increase of the size of the particles. Acidic "denaturation" of DNA within the compact particles (pH approximately 2.5) is followed by a dissappearance of the CD negative band and a considerable increase of the particle size. The data obtained indicate that the specific arrangement of DNA strands manifested in a CD negative band depends on the defects in the DNA secondary structure.
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PMID:[The compact form of DNA in solution. IV. The effect of secondary structure defectiveness on the arrangement of double-chained DNA molecules into compact particles]. 0 1

A stable and reproducible methemoglobinemia is induced by small concentration of an oxidizing gas (NO). Under such conditions we evidenced that plasma pH (pHe) to erythrocyte pH (pHi) relationship is unchanged. A strong acidity bound to the changes of NO in water occurs. But we may conclude that the buffer capacity of erythrocyte is not modified by the oxydation of ferro into ferrihemoglobin within the erythrocyte.
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PMID:Lack of effect of methemoglobinemia on the plasma-erythrocyte pH relationship. 1 49

During November and December 1975 frequent clotting occurred in the extracorporeal circuits of different dialyzers used in our unit. After installation of new automatically regenerating ion exchange resin columns,, the pH of deionized water ranged from 4.2 to 8.4 during 24 hr periods. Dialysate pH ranged between 5.3 and 8.2, and the patient's whole blood pHs ranged from 7.15 to 7.4 at the dialyzer inlet and from 6.2 (!) to 7.4 at the outlet. A strong correlation was seen between the acidity of the water and the frequency of clotting, and it was considered possible that the clotting was due to structural changes within the heparin molecules induced by the low pH. Following the introduction of an automatic titration device into our dialyzate preparation system, clotting with consecutive blood loss and subjective clinical symptoms have disappeared.
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PMID:Clotting in dialyzers due to low pH of dialysis fluid. 1 51

The effect of intravenous pentagrastin (4 microgram/kg-hr) on the rate of gastric emptying of solid food was studied in 6 normal men. A mean consisting of one 99mTc-tagged chicken liver mixed with beef stew and taken with 200 ml of water was followed on its passage through the gastrointestinal tract by intermittent scanning with a gamma camera. The rate of the linear gastric emptying pattern was slowed by pentagastrin in every individual. The pH and titratable acidity of the gastric contents were similar in the pentagastrin and the control infusions. Neutralization of the gastric contents with bicarbonate in the pentagastrin studies did not alter gastric emptying rates. The results indicate that pentagastrin slows gastric emptying of solid food in man by an effect apart from acid secretion. The myoelectrical correlates of such an observation are uncertain.
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PMID:Effect of pentagastrin infusion on gastric emptying rate of solid food in man. 2 4

The pH dependence of buffer catalysis of exchange of the C-4 amino protons of cyclic cytosine 2',3'-monophosphate (cCMP) and the N-1 proton of cyclic guanosine 2',3'-monophosphate (cGMP) conforms to an exchange mechanism, in which protonation of the nucleobases at C(N-3) AND G(N-7) establishes the important intermediates at neutral to acidic pH. Rate constants for transfer of the G(N-1) proton to H2O, OH-, phosphate, acetate, chloracetate, lactate, and cytosine (N-3) were obtained from 1H nuclear magnetic resonance line width measurements at 360 MHz and were used to estimate the pK or acidity of the exchange site in both the protonated and unprotonated nucleobase. These estimates reveal an increase in acidity of the G(N-1) site corresponding to 2 to 3 pK units as the G(N-7) site is protonated: At neutral pH the G(N-1) site of the protonated purine would be ionized (pK = 6.3). Determinations of phosphate, imidazole, and methylimidazole rate constants for transfer of the amino protons of cCMP provide a more approximate estimate of pK = 7 to 9 for the amino of the protonated pyrimidine. A comparison of the intrinsic amino acidity in the neutral and protonated cytosine is vitiated by the observation that OH- catalyzed exchange in the neutral base is not diffusion limited. This leads to the conclusion that protonation of the nucleobase effects a qualitative increase in the ability of the amino protons to form hydrogen bonds: from very poor in the neutral base to "normal" in the conjugate acid.
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PMID:Exchange mechanisms for hydrogen bonding protons of cytidylic and guanylic acids. 2 60

A comprehensive investigation of the interaction of Zn(II) and Co(II) with the dipeptide glycyl-L-tyrosine has been carried out. The carboxyl, amino, and tyrosyl pKa values, as well as the distribution of solution complexes, have been determined by analytical potentiometry. The amide pKa value was determined by relating the proton magnetic resonance (PMR) titration behavior of the tyrosyl alpha-hydrogen resonance to an H2-acidity function for concentrated solutions of aqueous base. Both metals behave in a qualitatively similar manner, yielding equivalent species as a function of pH. Both metals formed bis-peptide complexes, involving amino and peptide carbonyl coordination near pH = 8, with Zn(II) demonstrating a substantially higher affinity for the ligand. No evidence could be found for direct, metal-promoted phenolic dissociation, although the tyrosyl pKa value was sensitive to metal binding at other loci on the dipeptide molecule. At high pH, both systems ionized two additional protons. In the Co(II) system, these correspond to amide protons. However, it is not entirely clear whether the protons in the Zn(II) system originate from the peptide linkage or metal-bound water molecules.
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PMID:A comparative study of Zn(II) and Co(II) binding to glycyl-L-tyrosine, a pseudosubstrate for carboxypeptidase A. 3 45

An Aspergillus flavus strain isolated from Egyptian soil produced fat in appreciable amounts. General evidence for the operation of the tricarboxylic acid cycle in this organism has been ascertained by the detection of citric, malic and fumaric acids in the metabolized culture solution. Maximum fat yield was attained after seven days of incubation. The lower intial pH value of the media favoured the fat obtained from the felts and raised its acid value. When the felts were sterilized in their acidic metabolism solutions increased the acid values of the fats over those of fats extracted from felts sterilized in distilled water. The felts autoclaved for the longest time produced the highest yields of fat with the highest free acidity. The employment of calcium carbonate in the nutrient solutions raised appreciably the acid values of the fats and suppressed the other metabolic activities.
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PMID:Biosynthesis of fat in surface culture of a local strain of Aspergillus flavus. 4 Mar 64

Resistance to urea in vitro at 37 degrees C varied for each FMDV strain analysed. The urea marker did not correlate with other markers such as resistance to acid, resistance to acidity or size of plaques under agar on BHK21/13 cells. The resistance to urea of subtypes A24 Cruzeiro, O1 Caseros and C3 Resende varied in accordance with their antigenic potency when administered to swine as a trivalent water-in-oil emulsion type vaccine.
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PMID:Susceptibility of various FMDV strains to urea. 20 32

The effect of Jorpes secretin on the urinary volume, pH, and excretion of sodium, potassium, chloride, bicarbonate, titratable acidity, ammonia and phosphate was studied in five healthy male volunteers with and without simultaneous aspiration of duodenal fluids. A three- to fourfold increase in urinary volume and sodium excretion occurred within the first 30 min after secretin injection and this was accompanied by a significant rise in urinary pH in each instance. Urinary bicarbonate excretion increased from 55 plus or minus 13 to 395 plus or minus 33 mueq/30 min after secretin injection. Aspiration of alkaline duodenal contents was accompanied by an even greater postsecretin increase in urinary bicarbonate excretion. No significant changes in arterial pH or blood gases were detected throughout the study. These observations are compatible with a direct effect of secretin upon the renal tubular reabsorption of water, bicarbonate, and other ions, and could account for the transient alterations in urinary pH occurring in response to a meal.
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PMID:Renal response to secretin. 23 65


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