scholarly journals pH-dependent interconversion of two forms of tyrosinase in human skin

1988 ◽  
Vol 252 (2) ◽  
pp. 481-487 ◽  
Author(s):  
R K Tripathi ◽  
C Chaya Devi ◽  
A Ramaiah
Keyword(s):  
Human Skin ◽  
Sodium Phosphate ◽  
Inhibitory Concentration ◽  
Low Ph ◽  
The Other ◽  
Gradual Change ◽  
Ph Values ◽  
Sodium Phosphate Buffer ◽  
Solubilized Enzyme ◽  
Ph Dependent

1. We have shown that the characteristic lag in cresolase activity of human skin tyrosinase at inhibitory concentration of tyrosine was absent at all pH values studied, i.e. pH 5.2, 5.7, 6.2 and 6.8, if the enzyme solubilized at low pH was used as the source of enzyme, but the same enzyme when dialysed against buffers of various pH values showed linear activity only at pH 5.2 and was not inhibited by excess tyrosine, whereas at higher pH values it exhibited a lag and inhibition by excess tyrosine. 2. However, the enzyme solubilized in buffer/detergent, pH 6.8, when dialysed against buffer of the same pH showed linear activity at pH 5.2 and non-linear activity at pH 6.8. 3. The water/detergent-solubilized enzyme from human skin melanosomes showed linear activity even at inhibitory concentrations of tyrosine at pH 5.2 and 6.8 up to 2 h, but acceleration of rate was observed after 2 h for the enzyme measured at pH 6.8. 4. After dialysis of the water/detergent-solubilized enzyme against double-glass-distilled water, it still exhibits linear activity at inhibitory concentration of tyrosines at pH 6.8 for the first 2 h, but the same enzyme when dialysed against 0.02 M-sodium phosphate buffer, pH 6.8, exhibits negligible activity up to 1/2 h, in contrast with considerable activity before dialysis during the same interval of time, but without any loss of activity at later intervals of incubation time. 5. On the basis of these results, it is concluded that the enzyme exists in at least two interconvertible forms, one without lag and inhibition by excess tyrosine and the other with lag and inhibition by excess tyrosine. These two forms are interconvertible only by gradual change in pH over a period of hours.

Effect of pH on Glycolate and Ammonia Excretion in L-MSO Treated Chlorella Cells

1987 ◽  
Vol 42 (5) ◽  
pp. 525-529
Author(s):  
Yoshihiro Shiraiwa ◽  
Georg H. Schmid
Keyword(s):  
Chlorella Vulgaris ◽  
Major Part ◽  
Ammonia Excretion ◽  
Low Ph ◽  
Final Concentration ◽  
The Other ◽  
Effect Of Ph ◽  
Photosynthetic Rates ◽  
Ph Values ◽  
Glycolate Metabolism

Abstract The effect of pH changes on the excretion of ammonia and glycolate from algal cells into the medium was investigated in L-MSO (final concentration, 0.5 mм) -treated High-and Low CO2-cells of Chlorella vulgaris 211-11 h. The excretion was analyzed in the condition in which the cells were continuously gassed with air at 25 °C. At the values tested, generally more ammonia was excreted in L-MSO-treated Low CO2-cells than in L-MSO treated High CO2-cells. In both kinds of algal cells more ammonia was excreted at low pH-values and absolutely no ammonia was excreted at pH 8. In the dark, no or only slight ammonia excretion was observed in both L-MSO-treated High and Low CO2-cells. Under all these conditions no or only very low glycolate excretion was observed in both L-MSO treated High and Low CO2-cells. In High CO2-cells rates of photosynthesis were high at pH 6 and lower at higher pH values. On the other hand Low CO2-cells showed practically little dependence of photosynthetic rates on the pH. This result might indicate that the major part of the ammonia excretion observed, was not due to the inhibition of photosynthesis at acid pH values. It is known that ammonia excretion in L-MSO treated algal cells is due to the inhibition of the refixation of ammonia which originates from the glycine-serine aminotransferase reaction in the glycolate pathway. Our results demonstrate that glycolate production and glycolate metabolism are more intense at low pH values when compared to high pH values. This is valid for both High and Low CO2-cells. Low CO2-cells in Chlorella vulgaris 211-11 h exhibit a more active glycolate metabolism than High CO2-cells.

scholarly journals Variable H+/substrate stoicheiometries in Rhodotorula gracilis are caused by a pH-dependent protonation of the carrier(s)

1982 ◽  
Vol 208 (2) ◽  
pp. 459-464 ◽  
Author(s):  
R Hauer ◽  
M Höfer
Keyword(s):  
Positive Charge ◽  
Low Ph ◽  
The Other ◽  
Transport Systems ◽  
Lower Affinity ◽  
High Affinity ◽  
High Sugar ◽  
Saturation Kinetics ◽  
Rhodotorula Gracilis ◽  
Ph Dependent

Two carrier-mediated systems transport sugars in the yeast Rhodotorula gracilis depending on the pH. One system, with higher affinity for sugars, catalyses a symport of protons with sugar, whereas the other system, having lower affinity, is independent of protons. This was shown in three different ways. (1) At low pH, where only the high-affinity system works, a H+/sugar stoicheiometry of 1 was found. An increase of the pH and of the sugar concentration, which allowed the low-affinity system to operate, brought about a drop of the stoicheiometry to values below 1. (2) During H+ symport the influx of positive charge was electrically compensated by an equivalent efflux of K+ from the cells. At high pH and high sugar concentrations this stoicheiometry of K+ and sugar decreased concomitant with the H+/sugar stoicheiometry. (3) At pH 7.5 both transport systems were operating, as shown by biphasic saturation kinetics. Under these conditions only the high-affinity transport was found to be electrogenic. These results agree with the theory of an electrogenic H+/sugar symport where changes in the affinity for substrate are brought about by reversible protonation and deprotonation of the carrier.

scholarly journals Shelf life of minimally processed pineapples treated with ascorbic and citric acids

Bragantia ◽  
2012 ◽  
Vol 71 (3) ◽  
pp. 447-453 ◽  
Author(s):  
Lucimara Rogéria Antoniolli ◽  
Benedito Carlos Benedetti ◽  
Men de Sá Moreira de Souza Filho ◽  
Deborah dos Santos Garruti ◽  
Maria de Fátima Borges
Keyword(s):  
Ascorbic Acid ◽  
Shelf Life ◽  
Respiratory Activity ◽  
Low Ph ◽  
The Other ◽  
Water Control ◽  
Minimally Processed ◽  
Ph Values ◽  
Physical Chemical ◽  
Polyethylene Terephtalate

The purpose of this research was to determine the shelf life of minimally processed (MP) 'Pérola' pineapples treated with ascorbic acid (AA) and citric acid (CA) based on physical, chemical, sensorial and microbiological attributes. Slices were dipped into drinking water (control) or combined solutions of AA:CA (%) (1.0:0.5 and 1.0:1.0) with sodium hypochlorite (NaClO 20 mg L-1) for 30 seconds. The samples were conditioned in polyethylene terephtalate packages and stored at 4±1 °C per 13 days. The low peroxidase activity in the slices treated with antioxidant combinations was related to low pH values observed in these samples. The treatments 1.0:0.5 and 1.0:1.0 (AA:CA, %) favored maintenance of the initial a* values and avoided the pulp browning. The ascorbic acid increased more than double on the 2nd day in the treated slices. By the 4th day the CO2 values suggested a higher respiratory activity in the slices treated with anti-browning compounds. The antioxidant treatments did not produce detectable residual flavors in the MP pineapple. Regardless of microbiological safety during the 13 days of cold storage, the control slices can be kept by 6 days, afterwards the color and dehydration become strong enough to affect the appearance. On the other hand, MP 'Pérola' pineapples treated with 1.0:0.5 (AA:CA, %) and NaClO (20 mg L-1) can be stored for 8 days at 4±1 ºC, which represents the extension of the shelf life in 2 days. After this period the overripe odor starts to develop.

THE EFFECT OF NITROGEN AND PHOSPHORUS NUTRITION ON pH OF TOMATO

1966 ◽  
Vol 46 (6) ◽  
pp. 681-684 ◽  
Author(s):  
J. S. Matthews ◽  
L. G. Denby
Keyword(s):  
Low Ph ◽  
The Other ◽  
Phosphorus Nutrition ◽  
Nitrogen And Phosphorus ◽  
Tomato Fruits ◽  
High Ph ◽  
Ph Values ◽  
Low Levels ◽  
Nutrient Solutions

Tomato fruits, grown under glass in inert media, and supplied with nutrient solutions containing high and low levels of N and P, varied in pH from 4.21 to 4.61. Fruits from plants receiving low levels of both nutrients consistently had low pH values. Those from plants fed high levels of P or N had high pH whenever the level of the other element was not limiting.

scholarly journals Thermal denaturation in acidic solutions of double-helical ribonucleic acid from virus-like particles found in Penicillium chrysogenum. A spectrophotometric study

1971 ◽  
Vol 125 (2) ◽  
pp. 655-665 ◽  
Author(s):  
R. A. Cox ◽  
K. Kanagalingam ◽  
Elisabeth Sutherland
Keyword(s):  
Base Pair ◽  
Penicillium Chrysogenum ◽  
Sodium Phosphate ◽  
Thermal Denaturation ◽  
Spectrophotometric Study ◽  
Base Pairs ◽  
Native Form ◽  
Acidic Solutions ◽  
Ph Values ◽  
Sodium Phosphate Buffer

1. Two species of double-helical RNA isolated from mycelium of Penicillium chrysogenum were titrated with acid at 25°C and 95°C (solvent 0.1m-sodium phosphate buffer). At 25°C denaturation occurred at about pH3. At 95°C in the denatured form cytosine residues titrated as a simple monobasic acid of pK3.9 compared with pK≃2.5 for the native form at 25°C. 2. On thermal denaturation in neutral and acidic solutions one species of RNA (38% rG·rC) ‘melted’ in three distinct stages, equivalent to a mixture of three species, namely one of about 25% rG·rC, another of about 33% rG·rC and a third of about 46% rG·rC: the relative proportions were 0.25:0.35:0.40. 3. On thermal denaturation in acidic solutions the increase in the fraction of ionized cytosine residues concomitant with the ‘melting’ of rG·rC base pair also affects the spectrum especially at 280nm and serves to enhance the contribution of rG·rC base pairs at this wavelength. The increment in ε(P) at 280nm on ‘melting’ an rG·rC base pair approaches 53501·mol−1·cm−1 depending on pH, compared with 33501·mol−1·cm−1 at pH7. In contrast ε(P) at 280nm is scarcely affected by ‘melting’ rA·rU base pairs or by the protonization of adenine residues. 4. Changes in the spectrum of Escherichia coli rRNA on denaturation in acidic solutions were studied to yield the mole fractions of rA·rU and rG·rC base pairs ‘melting’ at particular pH values.

scholarly journals Evaluation of the ameliorative roles of Vitamins A, C and E on reduced glutathione in Clarias gariepinus (Burchell, 1822) fingerlings exposed to cadmium chloride

2021 ◽  
Vol 15 (3) ◽  
pp. 052-062
Author(s):  
Patrick Ozovehe Samuel ◽  
Francis Ofurum Arimoro ◽  
Adesola Victoria Ayanwale ◽  
Hadiza Lami Mohammad
Keyword(s):  
Phosphate Buffer ◽  
Sodium Phosphate ◽  
Cadmium Chloride ◽  
Reduced Glutathione ◽  
Clarias Gariepinus ◽  
The Other ◽  
Production Level ◽  
Water Medium ◽  
Sodium Phosphate Buffer ◽  
Aquarium Tank

Effects of cadmium chloride on the production of antioxidants such as reduced glutathione (GSH) in Clarias gariepinus and how such effects can be ameliorated through administration of vitamins were investigated. C. gariepinus fingerlings were exposed to sub-lethal concentrations of Cd (00, 12mg/L, 16mg/L, 20mg/L and 24mg/L) with replicate in each case. 12mg/L each of the vitamins were administered across all bud. Fresh concentrations of both toxicant and vitamins were administered every 72 hours for a period of 12 weeks every time the water medium was changed. 3 samples of the fish were randomly selected and sacrificed from each aquarium tank every 2 weeks. The gills, kidneys and liver were excised from these specimens, homogenized in sodium phosphate buffer and then assayed for GSH production levels in each case. From the results: In Cd only group, the highest GSH level produced in the liver was 38.85±0.07µg/ml. In the liver of samples of CdVA group, the value (93.97±0.07µg/ml) increased then followed by the gill (67.72±0.13µg/ml). In CdVC, the GSH production level in the gill (39.76±0.07µg/ml) was relatively higher than livers and kidneys of the samples. In CdVE, the kidney produced the highest GSH value of 32.89±0.10µg/ml. The elicitation and utilization of the antioxidant at one point or the other were adopted by the fish in dealing with the effects of the toxicant especially in the presence of the vitamins. Higher concentrations of the vitamins could facilitate the understanding of the effects of the vitamins in mitigating the effects of the toxicant.

Influence of pH on Cadmium Removal by Mineral Adsorbent

2012 ◽  
Vol 518-523 ◽  
pp. 3026-3029
Author(s):  
Chun Fang Tang ◽  
Ke Lin Li ◽  
Cheng Feng Li
Keyword(s):  
Low Ph ◽  
Langmuir Equation ◽  
Maximum Amount ◽  
Cadmium Removal ◽  
Ph Values ◽  
Adsorption Data ◽  
Dependent Model ◽  
Adsorption Amount ◽  
Ph Dependent ◽  
Influence Of Ph

The effect of pH on Cd adsorption was studied using red soil as an adsorbent in this study.The curve of Cd adsorbed vs pH showed that the adsorption amount increased slowly at low pH, then quickly with the increase of pH, and reached the maximum amount at high pH. The adsorption data at different pH values and initial Cd(II) concentrations were fitted well by Langmuir isotherm. At last, a pH-dependent model of adsorption isotherms of Cd was established by substituting the fitting results obtained from experimental data for the parameters in Langmuir equation.

Sorption of Lead and Cadmium on Ostsorb P and Ostsorb SA-5 Cellulose Sorbents

1992 ◽  
Vol 57 (10) ◽  
pp. 2089-2094 ◽  
Author(s):  
Ladislav Svoboda ◽  
Leona Čáňová
Keyword(s):  
Ionic Strength ◽  
Functional Groups ◽  
Cation Exchanger ◽  
Exchange Capacity ◽  
Low Ph ◽  
The Other ◽  
Ph Values ◽  
Lead And Cadmium ◽  
Acid Fragment ◽  
Bead Cellulose

The effect of pH and ionic strength on the exchange capacity of sorbents based on modified bead cellulose was examined for the sorption of Pb2+ and Cd2+ ions. Ion exchange of these cations in aqueous solutions is nonselective on Ostsorb SA-5, which is cellulose containing functional groups based on H-acid. The medium acidic Ostsorb P cation exchanger with functional groups formed by the phosphoric acid fragment, on the other hand, sorbs lead, and to a lesser extent also cadmium, also at high ionic strengths of the medium even at low pH values.

Response of Cultures of Propionibacterium to Acid and Low pH: Tolerance and Inhibition

1998 ◽  
Vol 61 (2) ◽  
pp. 211-216 ◽  
Author(s):  
JILL L. REHBERGER ◽  
BONITA A. GLATZ
Keyword(s):  
Hydrochloric Acid ◽  
Propionic Acid ◽  
Low Ph ◽  
The Other ◽  
Propionibacterium Acidipropionici ◽  
Ph Values ◽  
Neutral Ph ◽  
Ph Tolerance ◽  
Propionibacterium Thoenii ◽  
Ph Conditions

Seventeen Propionibacterium strains were tested for acid production and final pH achieved on glucose, fructose, or maltose as the primary carbon source. On average, strains of Propionibacterium acidipropionici produced more acid and reached lower final pH values than did strains of the other species. Three strains of P. acidipropionici, one Propionibacterium jensenii, and two Propionibacterium thoenii strains were tested further for the ability to survive and/or grow at low pH with lactic, hydrochloric, or propionic acid as acidulant. The organic acids were more inhibitory than hydrochloric acid; propionic acid was most inhibitory. In all cases, the P. jensenii and P. thoenii strains initiated growth and survived at lower pH values than did the P. acidipropionici strains. The ability to produce large amounts of acid or achieve low final pH values did not coincide with the ability to initiate growth or survive in low-pH conditions. Strains could not initiate growth below pH 5.0, but cultures started at neutral pH reached final pH values of less than 4.4. At neutral pH, strains could grow in the presence of increased lactate concentrations (up to 180 mM) or propionate concentrations (150 mM) that were inhibitory at acid pH. Attempts to isolate variants able to initiate growth below pH 5.0 were unsuccessful.

Cytotoxic properties of salivary oxidants

1990 ◽  
Vol 258 (1) ◽  
pp. C115-C121 ◽  
Author(s):  
M. B. Grisham ◽  
E. M. Ryan
Keyword(s):  
Membrane Permeability ◽  
Low Ph ◽  
Extracellular Ph ◽  
Human Erythrocytes ◽  
Acidic Ph ◽  
Cytotoxic Potential ◽  
Oxidize Glutathione ◽  
Ph Values ◽  
Ph Dependent ◽  
Conjugate Base

Salivary peroxidase and to a lesser extent myeloperoxidase are present in significant concentrations in saliva and catalyze the oxidation of thiocyanate anion (SCN-) by H2O2 to yield the potent oxidants hypothiocyanous acid (HOSCN) and its conjugate base hypothiocyanite anion (OSCN-). The objective of this study was to characterize the cytotoxic potential of peroxidase-generated HOSCN/OSCN- toward human erythrocytes. We found that HOSCN/OSCN- (0.25 mM) generated by the peroxidase-H2O2-SCN- system caused significant hemolysis at pH 6.0 but not at pH 6.5, 7.0, or 7.4. Erythrocyte hemoglobin (OxyHb) was oxidized to methemoglobin (MetHb) at all pH values tested; however, the rate of MetHb formation was dramatically increased at low pH and was not affected by inosine hexaphosphate, suggesting that hemoglobin was oxidized primarily by HOSCN. Concurrent with oxidation of hemoglobin (Hb), there was a pH-dependent consumption of HOSCN/OSCN- with more of the oxidant consumed at pH 6.0 compared with pH 6.5, 7.0, or 7.4. The enhanced oxidation of Hb at acidic pH was not due simply to increased membrane permeability by the uncharged species (HOSCN), since both erythrocyte lysate Hb and purified Hb were oxidized to the same extent at low pH as were intact erythrocytes. It is concluded that both OSCN- and HOSCN enter human erythrocytes where the protonated oxidant (HOSCN) mediates hemolysis and oxidizes OxyHb to MetHb, whereas both HOSCN and OSCN- oxidize glutathione (GSH). These data suggest that the extracellular pH may play an important role in modulating the cytotoxic properties of salivary oxidants.

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