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

The effect of storage at -20 degrees C and +2 degrees C on the pepsins of human gastric juice was assessed by quantitative assay and agar gel electrophoresis. Quantitative assays showed no significant loss of peptic activity at either temperature over periods of storage up to 3 weeks, and no correlation between change in peptic activity and the acidity of the gastric juice, although raising the pH of the gastric juice above pH 2 with buffers gave improved stability over gastric juice mixed with buffer of lower pH. At low pH, the addition of bovine serum albumin gave improved stability. Agar gel electrophoresis showed that the pepsins were all stable at -20 degrees C for several days or several weeks, but alterations occurred in the pepsin molecules after several months.
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PMID:The stability of human pepsins in stored gastric juice. 23 49

Studies have been made on the amino acid composition of electrophoretically homogeneous albumin and its main isoelectrically homogeneous fraction in two strains of hens and their hybrid. Serum albumin of hen and hybrid is characterized by higher total content of Asp and Glu residues as compared with that of the cock (137, 121, and 116 respectively) and lower content of Lys (59 against 66). The acidity of albumin increases in the line cock-hen-hybrid. With respect to its amino acid composition, the maternal serum albumin stands close to the hybrid one.
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PMID:[Amino acid composition of chicken serum albumin]. 66 8

Studies have been made on the amino acid composition of electrophoretically homogeneous albumin and its main isoelectrically homogeneous fraction in two strains of hens and their hybrid. Serum albumin of hen and hybrid is characterized by higher total content of Asp and Glu residues as compared with that of the cock (137, 121, and 116 respectively) and lower content of Lys (59 against 66). The acidity of albumin increases in the line cock-hen-hybrid. With respect to its amino acid composition, the maternal serum albumin stands close to the hybrid one.
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PMID:[Hemoglobin oxygen affinity in Mesocricetus auratus hamsters of different ages]. 66 10

Liver and kidney slices prepared 30min after intravenous injections of formaldehyde-treated 125I-labelled bovine serum albumin into mice degrade approx. 25-40% of the protein to a trichloroacetic acid-soluble form during 60min incubation at 37 degrees C. The presence of bicarbonate in Krebs-Ringer phosphate medium inhibited intracellular proteolysis, and similar results were obtained at pH5 or pH7 in kidney or liver slices. Cellular integrity was required to obtain substantial rates of proteolysis. This intralysosomal intracellular degradation of an exogenous protein was partially inhibited by inhibitors of oxidative ATP formation, such as cyanide, azide, 2,4-dinitrophenol and absence of oxygen. Arsenite and iodoacetamide were also effective inhibitors, but the effects of fluoride were variable. These results suggest that an energy requirement exists for intralysosomal proteolysis in intact cells and are consistent with the hypothesis that energy may be required to maintain intralysosomal acidity.
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PMID:An energy requirement for the degradation of intravenously injected 125I-labeled albumin in mouse liver and kidney slices. 66 41

Among the chief constituents of bronchial secretions, serum or mucus proteins and mucins are the parameters enabling definition of the functional state of the tracheo-bronchial mucosa. The use of bronchial detergents in normal subjects or subjects with moderate secretions leads to the study of physiological sputum or to definition of the evolution of chronic bronchitis. Results of immunoglobulins G and A dosages, values of IgA 7S/IgA 11S and of IgA/serum albumin ratio are reported. In the same way, the equilibrium of secretion of mucins estimated by the percentage of the different classes of mucins separated according to their acidity degree is an evaluation element of the evolution degree of chronic bronchitis. The studies of correlation between rheological properties and chemical structure of bronchial secretions are reported. They postulate an original concept on the use of mucolytics.
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PMID:[Bronchial secretions: biochemical study. Physiopathological aspects]. 693 6

A potentiometric difference titration (PDT) method is used to study the ionization behavior of the thiol group in bovine serum albumin and in the following less complex compounds: glutathione, cysteine, 2-mercaptoethanol, 3-mercaptopropionic acid, 2-mercaptoethylamine, cis-2-mercaptocyclobutylamine, 2-aminothiophenol, and 5-mercapto-2-nitrobenzoic acid. In the PDT method the pH dependence of the amount of protons released in the reaction RSH + CH3SO2SCH3 leads to RSSCH3 + CH3SO2- + H+ is measured in order to obtain the pH dependence of the molar proton content of the thiol (hu) relative to the molar proton content of its methylthio derivative (hm). The pH dependence of hu--hm reflects the ionization behavior of the thiol group and of other groups whose ionization is thermodynamically linked to that of the thiol group. Data presented here indicate that the ionization behavior of the single thiol group in albumin is strikingly different in the native and the urea-denatured proteins. Three ionizable groups appear to affect ionization of the thiol in the native protein whereas only one group appears to affect ionization of the thiol in the urea-denatured protein. Furthermore, the measured PDT curves are consistent with an abnormally high acidity (pK less than 5) for the thiol in native albumin and a normal acidity for the thiol in the urea-denatured protein. Comparisons of microscopic ionization constants determined for cysteine by using the PDT method with those determined by other methods indicate that the PDT method should be useful in characterizing the ionization behavior of thiol groups in proteins and other polyprotic substances.
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PMID:Determination of interactive thiol ionizations in bovine serum albumin, glutathione, and other thiols by potentiometric difference titration. 700 29

An analytical method to measure malondialdehyde (MDA) was developed. MDA was derivatized with N-methylhydrazine (NMH) to 1-methylpyrazole (1-MP). 1-MP was extracted and analyzed by capillary gas chromatography with nitrogen-phosphorus detection. Analyte concentration, pH, and matrix effects of 1-MP-spiked samples were investigated to determine optimal recovery conditions. Efficiencies for solid-phase extraction ranged from 95.6 +/- 0.9 to 81.6 +/- 3.5% compared to 75.0 +/- 6.4 to 67.5 +/- 9.6% for liquid-liquid extraction for 20 to 1 nmol/ml 1-MP-spiked samples, respectively. Solid-phase extraction of 1-MP was more effective than liquid-liquid extraction over a range of pH 2-8.5 and in various aqueous matrices. Addition of methanol to the matrix decreased the solid-phase extraction efficiency. Reaction yield at pH 2-8.5 showed full conversion of MDA to 1-MP following reaction with NMH. Recovery of bound MDA was investigated by incubating bovine serum albumin (BSA) spiked with MDA at 37 degrees C for 18 h and separating the free MDA and MDA-bound protein. The recovery of bound MDA from BSA increased by increasing the acidity and temperature. Specific applications of this method for biological samples are given for the analysis of endogenous MDA in the plasma and red blood cells of mice and the formation of MDA in ultraviolet-irradiated cells in culture.
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PMID:Analysis of malondialdehyde in biological samples by capillary gas chromatography. 797 60

We examined the suitability of nine organic buffers for studying calcium binding to albumin by equilibrium dialysis. Results obtained with defatted human serum albumin showed that 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) and 2-([tris(hydroxymethyl)methyl] amino)ethanesulfonic acid were superior. Scatchard analysis of the experimental data from an extensive study performed in HEPES at pH 7.4 and 20 degrees C revealed (putting n(i) = 1, i = 1-4) k1 = 367 L/mol, k2 = 314 L/mol, k3 = 291 L/mol, and k4 = 179 L/mol. The very weak binding was characterized as n5 = 10 and k5 = 40 L/mol. The results were also analyzed in terms of stoichiometric association constants. The constants K1 and K2 were calculated to be 1513 and 647 L/mol, respectively, whereas the other constants were considered undeterminable. pH studies showed that in the interval 6.8-7.4, binding was not influenced by changes in acidity. Increasing pH to above the physiological value resulted in increased binding. At pH 8.0, k1 was increased almost fourfold, whereas k2 and k3 were approximately doubled. These findings indicate that the neutral to basic transition is important for the calcium-binding properties of albumin. The transition is a reversible, gradual conformational change of the protein at pH 6-9.
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PMID:Quantitative analyses of the interaction between calcium ions and human serum albumin. 843 6

To characterize possible differences between the fluid-phase endocytosis (pinocytosis) of bovine serum albumin and the receptor-mediated endocytosis of asialo-orosomucoid (AOM) in isolated rat hepatocytes, both probes were conjugated to radioiodinated tyramine-cellobiose, [125I]TC. The use of these conjugates made it possible to measure the uptake and intracellular distribution of the intact proteins as well as of their acid-soluble, membrane-impermeant degradation products. [125I]TC-albumin was taken up at a very low rate (0.5%/h) compared to [125I]TC-AOM (45%/h), suggesting that neither membrane adsorption nor membrane permeation compromised its suitability as a fluid-phase marker. Sucrose gradient analysis indicated that both probes sequentially entered light endosomes (1.11 g/ml), dense endosomes (1.14 g/ml) and lysosomes (1.18 g/ml), but [125I]TC-albumin traversed the endocytic compartments more rapidly than [125I]TC-AOM, and was partially degraded intralysosomally already after 15 min. The microtubule inhibitor, vinblastine, had a stronger inhibitory effect on the uptake and degradation of [125I]TC-AOM (80% and 95%, respectively) than on the uptake and degradation of [125I]TC-albumin (50% and 70%, respectively). In the presence of vinblastine, [125I]TC-AOM was retained both in light and dense endosomes, whereas [125I]TC-albumin was retained in dense endosomes only, suggesting that the early steps of fluid-phase endocytosis were less critically dependent on microtubular function than the early steps of receptor-mediated endocytosis. A perturbant of vacuolar pH, propylamine, inhibited the degradation of both probes strongly (75-100%), as would be expected from its lysosomotropic effect. Propylamine also inhibited endocytic uptake, with a stronger effect on [125I]TC-AOM uptake (95% inhibition) than on [125I]TC-albumin uptake (60% inhibition), probably reflecting a reduction in endosomal acidity, reduced receptor-ligand dissociation and diminished recycling of free asialoglycoprotein receptors to the cell surface in addition to a general trapping of membrane in swollen vacuoles. A protein phosphatase inhibitor, okadaic acid, strongly (80-100%) inhibited the uptake and degradation of both [125I]TC-albumin and [125I]TC-AOM. An inhibitor of lysosomal proteinases, leupeptin, strongly suppressed the degradation of both probes and moderately reduced the uptake of [125I]TC-AOM, whereas the uptake of [125I]TC-albumin was unaffected. In contrast, an inhibitor of autophagic sequestration, 3-methyladenine, reduced both the uptake and degradation of [125I]TC-albumin markedly (55% and 75%, respectively), with considerably less effect on [125I]TC-AOM (25% and 35%, respectively). As autophagy-inhibitory amino acid mixture did not share these effects, suggesting that 3-methyladenine may suppress endocytic fluid-phase uptake by an autophagy-independent mechanism. Fluid-phase and receptor-mediated endocytosis in hepatocytes thus appear to differ with respect to uptake mechanisms as well as in the kinetics by which endocytosed material traverses the endocytic-lysosomal pathway.
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PMID:Differences between fluid-phase endocytosis (pinocytosis) and receptor-mediated endocytosis in isolated rat hepatocytes. 917 69

The Ehrlich reaction was optimized to determine pyrrolized proteins produced as a consequence of lipid peroxidation and oxidative stress. The procedure consisted of the treatment of the modified protein with p-(dimethylamino)benzaldehyde at a controlled acidity and temperature, and the determination of adducts produced against the blank obtained in the absence of the reagent. The extinction coefficient of Ehrlich adducts was calculated by using epsilon-N-pyrrolylnorleucine (Pnl) as standard and was 35,000 M-1 cm-1. The response was linear and reproducible within the range 0. 16-20 microM Pnl. The assay was applied to determination of pyrrole content in bovine serum albumin, bovine alpha-globulins, bovine gamma-globulins, and mixtures of them, incubated overnight with 1 mM of 4,5(E)-epoxy-2(E)-heptenal, obtaining results similar to those from determination of Pnl by capillary electrophoresis after basic hydrolysis of the protein. The method was also applied to pyrrole determination in bovine plasma proteins either incubated with epoxyalkenals, hydroxyalkenals, lipid hydroperoxides, and secondary products of lipid peroxidation, or oxidized with Fe3+/ascorbate. All these treatments produced pyrrolization of plasma proteins and all Ehrlich adducts gave very similar absorbance spectra with the exception of that produced in the treatment with hydroxyalkenals. The above results suggest that protein pyrrolization is a normal consequence of the lipid peroxidation process and of oxidative stress, and that Ehrlich adducts may be valid to determine this pyrrolization.
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PMID:A spectrophotometric method for the determination of proteins damaged by oxidized lipids. 975 Jan 27


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