scholarly journals The action of trialkyltin compounds on mitochondrial respiration. The effect of pH

1974 ◽  
Vol 138 (3) ◽  
pp. 349-357 ◽  
Author(s):  
Alan P. Dawson ◽  
Michael J. Selwyn
Keyword(s):  
Maximum Rate ◽  
Ph Dependence ◽  
Acid Value ◽  
Alkaline Ph ◽  
Free Medium ◽  
Succinate Oxidation ◽  
Ph Values ◽  
Acid Ph ◽  
Internal Ph ◽  
Ph Range

1. Inhibition of 2,4-dinitrophenol-stimulated respiration by trialkyltins is dependent on the presence of Cl− in the assay medium and is only apparent at acid pH values. It appears to be a result of the Cl−–OH− exchange mediated by trialkyltins. 2. In a KCl medium at alkaline pH values, the maximum rate of respiration produced by uncouplers is further increased by the presence of trialkyltins. 3. The inhibition of uncoupled succinate oxidation at acid pH values is not reversed by increasing the external substrate concentration, suggesting that depletion of intramitochondrial succinate is not an important factor in the inhibition. 4. It is suggested that the probable explanation for these observations is that in the presence of Cl− trialkyltins alter the internal pH to a more acid value and this directly affects the activity of one or more steps in succinate oxidation. 5. The oligomycin-like action of trialkyltins in a Cl−-free medium shows considerable pH-dependence over the pH range 6.6–7.6 in the presence of 10mm-phosphate, but very much less pH-dependence in the presence of 1mm-phosphate. 6. The binding of triethyltin to mitochondria shows a pK at pH6.3 and does not change greatly over the pH range 6.6–7.6. 7. It is suggested that the pH-dependence of the oligomycin-like action described by Coleman & Palmer (1971) is the result of the pH-dependence of the formation of a hydrophilic complex between trialkyltins and Pi.

Note: Influence of pH on the Extraction Yield and Functional Properties of Macadamia (Macadamia Integrofolia) Protein Isolates

2004 ◽  
Vol 10 (4) ◽  
pp. 263-267 ◽  
Author(s):  
P. S. Bora ◽  
D. Ribeiro
Keyword(s):  
Functional Properties ◽  
Extraction Yield ◽  
Emulsifying Properties ◽  
Alkaline Ph ◽  
Protein Isolates ◽  
Ph Values ◽  
Macadamia Nut ◽  
Isoelectric Ph ◽  
Ph Range ◽  
Influence Of Ph

Three protein isolates from de-fatted macadamia nut kernel flour were prepared by extraction at acidic (pH2.0), neutral (pH7.2 with 0.2M phosphate buffer containing 0.5MNaCl) and alkaline (pH12.0) conditions. Extraction at pH2.0 solubilised nearly 52.0% of the proteins present in defatted macadamia flour, while extraction with buffer (pH7.2) and alkaline pH (12.0) solubilised about 83.0% of proteins. The yield of isoelectrically precipitated protein from acidic extract (pH2.0, isolate A) was about 65.2% and from neutral (isolate B) and alkaline extracts (isolate C) was slightly over 83.0% which accounted for 33.7, 69.1 and 69.4% of the proteins present in defatted flour. The protein content of the isolates was 80.1, 92.1 and 92.0% in A, B and C isolates respectively. The functional properties of these isolates were significantly different. Isolate A presented better solubility at pH below isoelectric pH, isolate C at pH above isoelectric pH and isolate B intermediate solubility at the pH range studied. Isolate B showed best water and oil absorption capacities followed by isolate C and least by isolate A. For each isolate, the emulsifying properties were also significantly different at different pH values.

Proton-sulfate cotransport: external proton activation of sulfate influx into human red blood cells

1984 ◽  
Vol 247 (3) ◽  
pp. C247-C259 ◽  
Author(s):  
M. A. Milanick ◽  
R. B. Gunn
Keyword(s):  
Membrane Potential ◽  
Red Blood Cells ◽  
Blood Cells ◽  
Half Cycle ◽  
Ph Values ◽  
Human Red Blood Cells ◽  
Internal Ph ◽  
Ph Range ◽  
External Ph ◽  
Chloride Concentrations

Sulfate influx into human red blood cells was measured at 0 and 22 degrees C at several fixed external pH values between 3 and 10. These cells had normal internal pH and chloride concentrations so that sulfate influx was not limited by the efflux half-cycle reactions. The flux was a Michaelis-Menten function of sulfate concentration at each pH with K1/2SO4 = 4-10 mM. External protons activated influx 100-fold at a single site with a pK = 5.9 at 22 degrees C and 5.5 at 0 degrees C. This pK is similar to the value 5.99 +/- 0.3 for external proton binding to the sulfate-loaded transporter at 0 degrees C (J. Gen. Physiol. 79: 87-114, 1982). The flux was stilbene sensitive even in valinomycin-treated cells and was independent of membrane potential. This proton-activated influx appears to be proton-sulfate cotransport. At high pH there was a proton-independent flux that was membrane potential and stilbene sensitive. This proton-insensitive flux appears to be SO4(2-)/Cl- exchange or net sulfate influx. The sulfate influx over the entire pH range may be described in terms of an equation for the sum of the influxes through these two pathways on band 3.

MITOCHONDRIAL SWELLING AT ACID pH

1966 ◽  
Vol 44 (6) ◽  
pp. 695-706 ◽  
Author(s):  
Roberto Cereijq-Santaló
Keyword(s):  
Hydrochloric Acid ◽  
Maximum Rate ◽  
Liver Mitochondria ◽  
Inhibitory Effect ◽  
Buffering Capacity ◽  
Rat Liver Mitochondria ◽  
Isotonic Solution ◽  
Ph Values ◽  
Acid Ph ◽  
Protein Gel

The effect of variations of pH on swelling of rat liver mitochondria was studied.It was found that mitochondria swell at acid pH (5.0–6.0) when they are incubated in isotonic solution of potassium chloride. The extent of swelling increased with decreasing tonicity of the medium. However, mitochondria did not swell at acid pH when they were incubated in isotonic sucrose. The inhibitory effect of sucrose was partially released by the addition of electrolytes to the medium.When unbuffered suspensions of mitochondria with different pH values were prepared by the addition of hydrochloric acid or sodium hydroxide to the incubation medium, it was observed that the extent of swelling increased both with acidity (6.0 to 5.0) and with alkalinity (7.0 to 8.0).Titration of the unbuffered mitochondrial suspensions showed a maximum buffering capacity in the ranges of pH values where maximum rate of swelling occurred.These results suggest that the mitochondrion behaves as a combination of osmometer and protein gel.

scholarly journals Molecular Basis of pH and Ca2+ Regulation of Aquaporin Water Permeability

2004 ◽  
Vol 123 (5) ◽  
pp. 573-580 ◽  
Author(s):  
Karin L. Németh-Cahalan ◽  
Katalin Kalman ◽  
James E. Hall
Keyword(s):  
Water Permeability ◽  
Xenopus Oocytes ◽  
Ph Regulation ◽  
Ph Dependence ◽  
Ph Sensitivity ◽  
Alkaline Ph ◽  
Acid Ph ◽  
Outer Vestibule ◽  
Calmodulin Mutant ◽  
Aquaporin Family

Aquaporins facilitate the diffusion of water across cell membranes. We previously showed that acid pH or low Ca2+ increase the water permeability of bovine AQP0 expressed in Xenopus oocytes. We now show that external histidines in loops A and C mediate the pH dependence. Furthermore, the position of histidines in different members of the aquaporin family can “tune” the pH sensitivity toward alkaline or acid pH ranges. In bovine AQP0, replacement of His40 in loop A by Cys, while keeping His122 in loop C, shifted the pH sensitivity from acid to alkaline. In the killifish AQP0 homologue, MIPfun, with His at position 39 in loop A, alkaline rather than acid pH increased water permeability. Moving His39 to His40 in MIPfun, to mimic bovine AQP0 loop A, shifted the pH sensitivity back to the acid range. pH regulation was also found in two other members of the aquaporin family. Alkaline pH increased the water permeability of AQP4 that contains His at position 129 in loop C. Acid and alkaline pH sensitivity was induced in AQP1 by adding histidines 48 (in loop A) and 130 (in loop C). We conclude that external histidines in loops A and C that span the outer vestibule contribute to pH sensitivity. In addition, we show that when AQP0 (bovine or killifish) and a crippled calmodulin mutant were coexpressed, Ca2+ sensitivity was lost but pH sensitivity was maintained. These results demonstrate that Ca2+ and pH modulation are separable and arise from processes on opposite sides of the membrane.

Mechanisms of inorganic carbon acquisition in two Euglena species

2005 ◽  
Vol 83 (7) ◽  
pp. 865-871 ◽  
Author(s):  
Brian Colman ◽  
Konstantine D Balkos
Keyword(s):  
Euglena Gracilis ◽  
Inorganic Carbon ◽  
Bicarbonate Transport ◽  
Alkaline Ph ◽  
Internal Ph ◽  
Bicarbonate Uptake ◽  
Acid Tolerant ◽  
Euglena Mutabilis ◽  
Ph Range ◽  
External Ph

The mechanism of inorganic carbon uptake was examined in Euglena gracilis Klebs. and the acidophilic species Euglena mutabilis Schmitz. Both species, whether grown in acidic (pH 3.5) or alkaline (pH 7.5) media lack external carbonic anhydrase. Acid-grown E. gracilis was shown to have no capacity for bicarbonate transport, but transport was induced on transfer to alkaline medium (pH 7.5) in the light over a period of 8 h. In contrast, acid-grown E. mutabilis appears to have no capacity for bicarbonate transport even at neutral pH. The overall internal pH of the cells was determined by equilibration with 14C-labelled benzoic acid over the pH range 3.5–5.0 and with 14C-labelled 5,5-dimethyloxazolidine-2,4-dione over the range pH 5.5–7.5. The acidophilic species maintains an internal pH range of 6.6–6.8 in an external pH range of 3.5–5.5, whereas the acid-tolerant species E. gracilis maintains a neutral internal pH in an external pH range of 3.5–7.5. Measurement, by mass spectrometry, of the fluxes of CO2 and O2 in photosynthesizing cells at pH 3.5 demonstrated a rapid uptake of CO2 by both species that was completely blocked by iodoacetamide, an inhibitor of CO2 fixation. Uptake of CO2 by E. gracilis, grown at pH 7.5, was not completely inhibited by iodoacetamide and O2 evolution was sustained when the cells reached the CO2 compensation concentration, indicating a direct uptake of bicarbonate. These data indicate that the acidophilic species, E. mutabilis, takes up CO2 by diffusion, whereas the acid-tolerant species, E. gracilis, takes up CO2 by diffusion at acid pH levels but has some capacity for active bicarbonate uptake when grown at alkaline pH levels.Key words: acidophilic alga, acidotolerant alga, bicarbonate uptake, CO2 uptake, Euglena gracilis, Euglena mutabilis, internal pH.

Magnetite Sorption Capacity for Strontium as a Function of pH

2008 ◽  
Vol 1107 ◽  
Author(s):  
Joan de Pablo ◽  
Miquel Rovira ◽  
Javier Giménez ◽  
Ignasi Casas ◽  
Frederic Clarens
Keyword(s):  
Spent Nuclear Fuel ◽  
Surface Complexation ◽  
Retardation Factor ◽  
Alkaline Ph ◽  
Layer Model ◽  
Surface Complexation Model ◽  
Ph Values ◽  
End Products ◽  
Diffuse Layer Model ◽  
Ph Range

AbstractThe ubiquity of iron oxide minerals and their ability to retain metals on their surface can represent an important retardation factor to the mobility of radionuclides. In a deep repository for the spent nuclear fuel, the intrusion of the groundwater might produce the anoxic corrosion of the iron, with magnetite as one of the end-products. In this study, as expected considering the strontium speciation in solution, strontium is sorbed onto magnetite at alkaline pH values while at acidic pH the sorption is negligible. Magnetite is able to sorb more than the 50% of the strontium from a 8·10-6 mol·dm-3 solution at the pH range representative of most groundwater (7-9). A surface complexation model has been applied to the experimental data, allowing to explain the results using the Diffuse Layer Model (DLM) and considering the formation of the inner-sphere complex >FeOHSr2+ (with a calculated logK=2.7±0.3). Considering these data, the magnetite capacity to retain strontium and other radionuclides is discussed

scholarly journals Diversity and Mechanisms of Alkali Tolerance in Lactobacilli

2007 ◽  
Vol 73 (12) ◽  
pp. 3909-3915 ◽  
Author(s):  
Yuki Sawatari ◽  
Atsushi Yokota
Keyword(s):  
Plant Material ◽  
Lactobacillus Casei ◽  
Glucose Utilization ◽  
Ph Values ◽  
Internal Ph ◽  
Alkali Tolerance ◽  
Ph Range ◽  
High Alkali ◽  
External Ph

ABSTRACT We determined the maximum pH that allows growth (pHmax) for 34 strains of lactobacilli. High alkali tolerance was exhibited by strains of Lactobacillus casei, L. paracasei subsp. tolerans, L. paracasei subsp. paracasei, L. curvatus, L. pentosus, and L. plantarum that originated from plant material, with pHmax values between 8.5 and 8.9. Among these, L. casei NRIC 1917 and L. paracasei subsp. tolerans NRIC 1940 showed the highest pHmax, at 8.9. Digestive tract isolates of L. gasseri, L. johnsonii, L. reuteri, L. salivarius subsp. salicinius, and L. salivarius subsp. salivarius exhibited moderate alkali tolerance, with pHmax values between 8.1 and 8.5. Dairy isolates of L. delbrueckii subsp. bulgaricus, L. delbrueckii subsp. lactis, and L. helveticus exhibited no alkali tolerance, with pHmax values between 6.7 and 7.1. Measurement of the internal pH of representative strains revealed the formation of transmembrane proton gradients (ΔpH) in a reversed direction (i.e., acidic interior) at alkaline external-pH ranges, regardless of their degrees of alkali tolerance. Thus, the reversed ΔpH did not determine alkali tolerance diversity. However, the ΔpH contributed to alkali tolerance, as the pHmax values of several strains decreased with the addition of nigericin, which dissipates ΔpH. Although neutral external-pH values resulted in the highest glycolysis activity in the presence of nigericin regardless of alkali tolerance, substantial glucose utilization was still detected in the alkali-tolerant strains, even in a pH range of between 8.0 and 8.5, at which the remaining strains lost most activity. Therefore, the alkali tolerance of glycolysis reactions contributes greatly to the determination of alkali tolerance diversity.

scholarly journals Expression of Outer Membrane Proteins inEscherichia coli Growing at Acid pH

2000 ◽  
Vol 66 (3) ◽  
pp. 943-947 ◽  
Author(s):  
Mikiko Sato ◽  
Kazuhiro Machida ◽  
Eri Arikado ◽  
Hiromi Saito ◽  
Tomohito Kakegawa ◽  
...  
Keyword(s):  
Outer Membrane Proteins ◽  
Optimal Growth ◽  
Alkaline Media ◽  
Alkaline Ph ◽  
Two Component System ◽  
E Coli ◽  
Ph Values ◽  
Acid Ph ◽  
Medium Osmolarity ◽  
Two Component

ABSTRACT It is generally accepted for Escherichia coli that (i) the level of OmpC increases with increased osmolarity when cells are growing in neutral and alkaline media, whereas the level of OmpF decreases at high osmolarity, and that (ii) the two-component system composed of OmpR (regulator) and EnvZ (sensor) regulates porin expression. In this study, we found that OmpC was expressed at low osmolarity in medium of pH below 6 and that the expression was repressed when medium osmolarity was increased. In contrast, the expression of ompF at acidic pH was essentially the same as that at alkaline pH. Neither OmpC nor OmpF was detectable in anompR mutant at both acid and alkaline pH values. However, OmpC and OmpF were well expressed at acid pH in a mutantenvZ strain, and their expression was regulated by medium osmolarity. Thus, it appears that E. coli has a different mechanism for porin expression at acid pH. A mutant deficient in ompR grew slower than its parent strain in low-osmolarity medium at acid pH (below 5.5). The same growth diminution was observed when ompC and ompF were deleted, suggesting that both OmpF and OmpC are required for optimal growth under hypoosmosis at acid pH.

Effect of pH on phosphate transport into intestinal brush-border membrane vesicles

1984 ◽  
Vol 246 (2) ◽  
pp. G180-G186 ◽  
Author(s):  
G. Danisi ◽  
H. Murer ◽  
R. W. Straub
Keyword(s):  
Brush Border ◽  
Brush Border Membrane ◽  
Ph Dependence ◽  
Membrane Vesicles ◽  
Sodium Concentration ◽  
Brush Border Membrane Vesicles ◽  
Alkaline Ph ◽  
Effect Of Ph ◽  
Ph Values ◽  
Sodium Dependent

The effect of pH on the rate of phosphate (Pi) uptake was studied in rabbit duodenal brush-border membrane vesicles. Pi uptake was found to be sodium dependent at all pH values tested (5.7-8.1). Further, the rate of Pi uptake depended on pH; for instance, with 100 mM external sodium, reducing the pH from 8.1 to 6.8 or 5.7 doubled the rate of Pi influx. At 100 mM external sodium, experiments under initial rate conditions, carried out with varying Pi concentrations and at pH values of 6, 6.8, or 7.6, showed that sodium-dependent Pi uptake was saturable at the three pH values tested; the apparent Km expressed in function of total Pi was not dependent on pH. Vmax was not affected between pH 6 and 6.8 but was significantly reduced at pH 7.6. Lowering external sodium lowered Vmax at all pH values investigated. At acid and alkaline pH the rate of Pi uptake was a sigmoidal function of the external sodium concentration. Hill coefficients, calculated from these experiments, exceeded unity and were unaffected by pH. At saturating sodium concentrations, the rate of Pi uptake was higher at pH 6 than at pH 7.6. The [Na]0.5 was lower at pH 7.6 than at pH 6. Further, sodium-dependent Pi uptake appeared to be electrogenic at acid and alkaline pH. It is concluded that the pH dependence of intestinal Pi transport is not an expression of preferential transport of monovalent or divalent phosphate. The pH dependence appears to reflect properties of the sodium-phosphate cotransport mechanism and is in part related to changes in the affinity of the transport system for sodium.

scholarly journals pH dependence of the acetylcholine receptor channel: a species variation.

1981 ◽  
Vol 77 (6) ◽  
pp. 647-666 ◽  
Author(s):  
E M Landau ◽  
B Gavish ◽  
D A Nachshen ◽  
I Lotan
Keyword(s):  
Rana Pipiens ◽  
Single Channel ◽  
Noise Analysis ◽  
Ph Dependence ◽  
Model Parameters ◽  
Species Variation ◽  
Rana Ridibunda ◽  
Alkaline Ph ◽  
Endplate Current ◽  
Acid Ph

The effects of pH changes on the miniature endplate current (mepc) and on endplate current fluctuations (acetylcholine [ACh] noise) were examined at the neuromuscular junction in vitro in two species of frogs. In Rana pipiens the relationship between the decay time constant of the mepc (tau') and pH had a symmetrical bell shape; the value of tau' being largest at pH 7 and decreasing at more acid or more alkaline pH. In acid pH the mepc amplitude (A) decreased relative to its value at pH 7, and in alkaline pH A increased. In Rana ridibunda a narrower and asymmetric bell-shaped dependence of tau' on pH, having a maximum of pH 5.5, was found. The mepc amplitude was again reduced in acid pH but had a peak at pH 5.5. Also, its value at pH 9 was larger than at pH 7. These results were obtained with a number of different buffers and were not found to be sensitive to the nature of the buffer chosen. By performing ACh-noise analysis we found that in Rana pipiens at acid pH (5.5-5.0), the single channel conductance (gamma) and the single channel open time (tau) were significantly reduced relative to their value at pH 7. However, in Rana ridibunda at acid pH (5.4) gamma was unchanged and tau was markedly increased relative to their values at pH 7. The results can be explained quantitatively by electrostatic interaction between two fixed and titratable ionic groups and a mobile charge in the receptor molecule. The model fits the data for groups having pKs approximately 4.8 and approximately 9.8 for Rana pipiens and approximately 4.6 and approximately 6.3 for Rana ridibunda. The groups can be tentatively identified as amino acid residues; glutamic or aspartic and lysine or tyrosine for Rana pipiens; glutamic or aspartic and histidine for Rana ridibunda. The difference in the fitted values of the other model parameters for these two species can be attributed to differences in the spatial configuration of the charged groups.

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