Investigation of the pH dependence of the kinetics of quartz dissolution at 25 °C

The pH of skin is critical for skin health and resilience and plays a key role in controlling the skin microbiome. It has been well reported that under dysbiotic conditions such as atopic dermatitis (AD), eczema, etc. there are significant aberrations of skin pH, along with a higher level of Staphylococcus aureus compared to the commensal Staphylococcus epidermidis on skin. To understand the effect of pH on the relative growth of S. epidermidis and S. aureus , we carried out simple in vitro growth kinetic studies of the individual microbes under varying pH conditions. We demonstrated that the growth kinetics of S. epidermidis is relatively insensitive to pH within the range of 5–7, while S. aureus shows a stronger pH dependence in that range. Gompertz’s model was used to fit the pH dependence of the growth kinetics of the two bacteria and showed that the equilibrium bacterial count of S. aureus was the more sensitive parameter. The switch in growth rate happens at a pH of 6.5–7. Our studies are in line with the general hypothesis that keeping the skin pH within an acidic range is advantageous in terms of keeping the skin microbiome in balance and maintaining healthy skin.

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Kinetics of the oxidation of reduced nicotinamide adenine dinucleotide by horseradish peroxidase compounds I and II

Biochemistry and Cell Biology ◽

10.1139/o86-045 ◽

1986 ◽

Vol 64 (4) ◽

pp. 323-327 ◽

Cited By ~ 13

Author(s):

Mohammed A. Kashem ◽

H. Brian Dunford

Keyword(s):

Horseradish Peroxidase ◽

Active Site ◽

Nicotinamide Adenine Dinucleotide ◽

Ph Dependence ◽

Transient State ◽

Nicotinamide Adenine ◽

Compound I ◽

Single Ionization ◽

Reduced Nicotinamide Adenine Dinucleotide ◽

Kinetics Of

The transient state kinetics of the oxidation of reduced nicotinamide adenine dinucleotide (NADH) by horseradish peroxidase compound I and II (HRP-I and HRP-II) was investigated as a function of pH at 25.0 °C in aqueous solutions of ionic strength 0.11 using both a stopped-flow apparatus and a conventional spectrophotometer. In agreement with studies using many other substrates, the pH dependence of the HRP-I–NADH reaction can be explained in terms of a single ionization of pKa = 4.7 ± 0.5 at the active site of HRP-I. Contrary to studies with other substrates, the pH dependence of the HRP-H–NADH reaction can be interpreted in terms of a single ionization with pKa of 4.2 ± 1.4 at the active site of HRP-II. An apparent reversibility of the HRP-II–NADH reaction was observed. Over the pH range of 4–10 the rate constant for the reaction of HRP-I with NADH varied from 2.6 × 105 to5.6 × 102 M−1 s−1 and of HRP-II with NADH varied from 4.4 × 104 to 4.1 M−1 s−1. These rate constants must be taken into consideration to explain quantitatively the oxidase reaction of horseradish peroxidase with NADH.

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Oxidation of Nickel(II) and Manganese(II) by Peroxodisulfate in Aqueous Solution in the Presence of Molybdate. Crystal Structure of the (NH4)6[NiMo9O32].6H2O Product

Australian Journal of Chemistry ◽

10.1071/ch9921943 ◽

1992 ◽

Vol 45 (12) ◽

pp. 1943 ◽

Cited By ~ 12

Author(s):

SJ Dunne ◽

RC Burns ◽

GA Lawrance

Keyword(s):

Rate Constant ◽

Linear Dependence ◽

Ph Dependence ◽

Order Rate Constant ◽

X Ray Diffraction ◽

X Ray ◽

First Order ◽

Oxidant Concentration ◽

Ph Range ◽

Kinetics Of

Oxidation of Ni2+,aq, by S2O82- to nickel(IV) in the presence of molybdate ion, as in the analogous manganese system, involves the formation of the soluble heteropolymolybdate anion [MMogO32]2- (M = Ni, Mn ). The nickel(IV) product crystallized as (NH4)6 [NiMogO32].6H2O from the reaction mixture in the rhombohedra1 space group R3, a 15.922(1), c 12.406(1) � ; the structure was determined by X-ray diffraction methods, and refined to a residual of 0.025 for 1741 independent 'observed' reflections. The kinetics of the oxidation were examined at 80 C over the pH range 3.0-5.2; a linear dependence on [S2O82-] and a non-linear dependence on l/[H+] were observed. The influence of variation of the Ni/Mo ratio between 1:10 and 1:25 on the observed rate constant was very small at pH 4.5, a result supporting the view that the precursor exists as the known [NiMo6O24H6]4- or a close analogue in solution. The pH dependence of the observed rate constant at a fixed oxidant concentration (0.025 mol dm-3) fits dequately to the expression kobs = kH [H+]/(Ka+[H+]) where kH = 0.0013 dm3 mol-1 s-1 and Ka = 4-0x10-5. The first-order dependence on peroxodisulfate subsequently yields a second-order rate constant of 0.042 dm3 mol-1 s-1. Under analogous conditions, oxidation of manganese(II) occurs eightfold more slowly than oxidation of nickel(II), whereas oxidation of manganese(II) by peroxomonosulfuric acid is 16-fold faster than oxidation by peroxodisulfate under similar conditions.

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The pKa of the catalytic histidine residue of chloramphenicol acetyltransferase

Biochemical Journal ◽

10.1042/bj2900015 ◽

1993 ◽

Vol 290 (1) ◽

pp. 15-19 ◽

Cited By ~ 7

Author(s):

A Lewendon ◽

W V Shaw

Keyword(s):

Chemical Modification ◽

Ph Dependence ◽

Thiol Group ◽

Chloramphenicol Acetyltransferase ◽

Histidine Residue ◽

Pka Values ◽

Primary Hydroxy Group ◽

Pka Value ◽

Catalytic Role ◽

Kinetics Of

A catalytically essential histidine residue (His-195) of chloramphenicol acetyltransferase (CAT) acts as a general base in catalysis, abstracting a proton from the primary hydroxy group of chloramphenicol. The pKa of His-195 has been determined from the pH-dependence of chemical modification. Both methyl 4-nitrobenzenesulphonate and iodoacetamide inactivate CAT by irreversible modification of His-195. The kinetics of inactivation by methyl 4-nitrobenzenesulphonate are pseudo-first-order, and the pH-dependence of inactivation yields a pKa value of 6.60. Iodoacetamide inactivation proceeds with second-order kinetics and a pKa value of 6.80. An alternative site of modification at the active site of CAT is the thiol group of Cys-31, a residue which has no catalytic role. On replacement of Cys-31 with alanine (Ala-31 CAT), the pH-dependence of iodoacetamide inactivation gives a pKa value of 6.66. The pKa values derived from chemical-modification experiments directed at His-195 are in agreement with the pKa values of 6.62 and 6.61 determined for wild-type and Ala-31 CAT respectively from the pH-dependence of kcat/Km.

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Kinetik der Reaktion von 2.4-Dinitrofluorbenzol mit Imidazol-, SH- und Imidazol-SH-Verbindungen / Kinetics of the Reaction of 2,4-dinitro-1-fluorobenzene with Imidazole-, SH- and Imidazole-SH-compounds

Zeitschrift für Naturforschung B ◽

10.1515/znb-1971-1011 ◽

1971 ◽

Vol 26 (10) ◽

pp. 1010-1016 ◽

Cited By ~ 2

Author(s):

Renate Voigt ◽

Helmut Wenck ◽

Friedhelm Schneider

Keyword(s):

Temperature Dependence ◽

Rate Constants ◽

Reaction Rate ◽

Ph Dependence ◽

First Order ◽

Molecular Transfer ◽

Thiolate Anion ◽

Nucleophilic Reactivity ◽

Kinetics Of ◽

Lindley Equation

First order rate constants of the reaction of a series of SH-, imidazole- and imidazole/SH-compounds with FDNB as well as their pH- and temperature dependence were determined. Some of the tested imidazole/SH-compounds exhibit a higher nucleophilic reactivity as is expected on the basis of their pKSH-values. This enhanced reactivity is caused by an activation of the SH-groups by a neighbouring imidazole residue. The pH-independent rate constants were calculated using the Lindley equation.The kinetics of DNP-transfer from DNP-imidazole to SH-compounds were investigated. The pH-dependence of the reaction displays a maximum curve. Donor in this reaction is the DNP-imidazolecation and acceptor the thiolate anion.The reaction rate of FDNB with imidazole derivatives is two to three orders of magnitude slower than with SH-compounds.No inter- or intra-molecular transfer of the DNP-residue from sulfure to imidazole takes place.

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Nitroalkanes as Reductive Substrates for Flavoprotein Oxidases

Zeitschrift für Naturforschung B ◽

10.1515/znb-1972-0914 ◽

1972 ◽

Vol 27 (9) ◽

pp. 1052-1053 ◽

Cited By ~ 16

Author(s):

David J. T. Porter ◽

Judith G. Voet ◽

Harold J. Bright

Keyword(s):

Hydrogen Peroxide ◽

Amino Acid ◽

Glucose Oxidase ◽

Ph Dependence ◽

Kinetic Mechanism ◽

Acid Oxidase ◽

Amino Acid Oxidase ◽

Kinetics Of ◽

Oxidase Reaction ◽

Detailed Kinetic Mechanism

Nitroalkanes have been found to be general reductive substrates for D-amino acid oxidase, glucose oxidase and L-amino acid oxidase. These enzymes show different specificities for the structure of the nitroalkane substrate.The stoichiometry of the D-amino acid oxidase reaction is straightforward, consisting of the production of one mole each of aldehyde, nitrite and hydrogen peroxide for each mole of nitroalkane and oxygen consumed. The stoichiometry of the glucose oxidase reaction is more complex in that less than one mole of hydrogen peroxide and nitrite is produced and nitrate and traces of 1-dinitroalkane are formed.The kinetics of nitroalkane oxidation show that the nitroalkane anion is much more reactive in reducing the flavin than is the neutral substrate. The pH dependence of flavin reduction strongly suggests that proton abstraction is a necessary event in catalysis. A detailed kinetic mechanism is presented for the oxidation of nitroethane by glucose.It has been possible to trap a form of modified flavin in the reaction of D-amino acid oxidase with nitromethane from which oxidized FAD can be regenerated in aqueous solution in the presence of oxygen.

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Effects of gas composition and pH on kinetics of lung angiotensin-converting enzyme

Journal of Applied Physiology ◽

10.1152/jappl.1987.62.3.1216 ◽

1987 ◽

Vol 62 (3) ◽

pp. 1216-1221 ◽

Cited By ~ 3

Author(s):

D. A. Rickaby ◽

R. D. Bongard ◽

M. J. Tristani ◽

J. H. Linehan ◽

C. A. Dawson

Keyword(s):

Angiotensin Converting Enzyme ◽

Surface Area ◽

Ph Dependence ◽

Gas Composition ◽

Converting Enzyme ◽

Hydrolysis Process ◽

Hypoxic Vasoconstriction ◽

Ace Activity ◽

Kinetics Of ◽

Hydrolysis Of

Given the pH dependence of enzymes in general and the potential importance of a blood and alveolar gas composition dependency on the interpretation of changes in the hydrolysis of angiotensin-converting enzyme (ACE) substrates by pulmonary endothelial ACE, we examined the influence of Pco2 and Po2 on the hydrolysis of a synthetic ACE substrate (benzoyl-phenylalanyl-alanyl-proline, BPAP) on passage through isolated rabbit lungs. Perfusate pH values of about 7.1, 7.4, and 7.9 were obtained by ventilating the lungs with gas containing different CO2 concentrations and Po2 values of approximately 110 and approximately 10 Torr were obtained by varying the concentration of O2 in the ventilating gas mixture. In the range studied neither acidosis nor alkalosis produced any significant changes in BPAP hydrolysis or in the kinetic parameters, Vmax and Km, for the hydrolysis process. On the other hand, a reduction in BPAP hydrolysis was detected when the Po2 was reduced from 110 to 10 Torr. The Vmax for BPAP hydrolysis by the lung was inversely correlated with the magnitude of the hypoxic vasoconstriction that occurred, suggesting that the reduced BPAP hydrolysis with hypoxia was due to the loss of perfused surface area due to the vasoconstriction. The results suggest that correlations between Pco2 and/or pH and whole-lung ACE activity that might occur in diseased lungs do not imply causalty. The hemodynamic consequences of changing Po2 (i.e., hypoxic vasoconstriction) may alter whole-organ ACE activity in the sense of changing the perfused surface area (i.e., the amount of ACE in contact with flowing perfusate).

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