Contribution to the knowledge of the role of SH-groups in the molecule of pea alcohol dehydrogenase

1985 ◽  
Vol 50 (9) ◽  
pp. 2015-2020
Author(s):  
Noemi Čeřovská ◽  
Sylva Leblová
Keyword(s):  
Alcohol Dehydrogenase ◽  
Active Center ◽  
Protective Action ◽  
First Order ◽  
Sh Groups ◽  
Coenzyme Binding ◽  
First Order Kinetics ◽  
Sh Group ◽  
Pea Seeds

p-Chloromercuribenzoate irreversibly inactivates alcohol dehydrogenase (ADH) isolated from germinating pea seeds. The reaction follows the first order kinetics. The inactivation of pea ADH is pH-dependent and is maximal at pH 9.0. NAD protects the enzyme from inactivation by p-chloromercuribenzoate; the higher the concentration of the coenzyme and the longer the period of incubation of NAD with the enzyme, the lower the degree of inactivation. Ethanol does not prevent the enzyme from inactivation. o-Phenanthroline in a concentration of 1 . 10-3 mol l-1 decreases the degree of inactivation of the enzyme by p-chloromercuribenzoate by 20%; imidazole is without effect on the reaction. Zn2+-ions in concentration of 1 . 10-5 mol l-1 also partly protect the enzyme from inactivation by p-chloromercuribenzoate. The results obtained show that the SH-groups sensitive to labeling with p-chloromercuribenzoate are localized in the active center of the enzyme, probably in the coenzyme-binding site. The protective action of Zn2+-ions and of o-phenanthroline against this inactivation confirms the assumption that the SH-group acts as a zinc ligand in the active center of the enzyme.

scholarly journals The role of histidine-118 of inorganic pyrophosphatase from thermophilic bacterium PS-3

1991 ◽  
Vol 278 (2) ◽  
pp. 595-599 ◽  
Author(s):  
N Hirano ◽  
T Ichiba ◽  
A Hachimori
Keyword(s):  
Thermophilic Bacterium ◽  
Complete Loss ◽  
Inorganic Pyrophosphatase ◽  
Histidine Residue ◽  
First Order ◽  
Diethyl Pyrocarbonate ◽  
Lysyl Endopeptidase ◽  
First Order Kinetics ◽  
Pseudo First Order

Treatment of the inorganic pyrophosphatase from thermophilic bacterium PS-3 with diethyl pyrocarbonate resulted in the almost complete loss of its activity, which followed pseudo-first-order kinetics. The presence of Mg2+ prevented the inactivation. Enzyme inactivated with diethyl pyrocarbonate was re-activated by hydroxylamine. The inactivation parallelled the amount of modified histidine residue, and a plot of the activity remaining against the amount of modified histidine residue suggested that the modification of one of two histidine residues totally inactivated the enzyme. The site involved was found to be located in a single lysyl endopeptidase-digest peptide derived from the ethoxy[14C]carbonylated enzyme. Amino acid analysis and sequence analysis of the peptide revealed that it comprised residues 96-119 of the inorganic pyrophosphatase from thermophilic bacterium PS-3. These results, when compared with those reported for the Escherichia coli and yeast enzymes, imply that His-118 of the inorganic pyrophosphatase from thermophilic bacterium PS-3 is located near the Mg(2+)-binding site and thus affects the binding of Mg2+.

scholarly journals Pyruvate and ketone-body transport across the mitochondrial membrane. Exchange properties, pH-dependence and mechanism of the carrier

1978 ◽  
Vol 172 (3) ◽  
pp. 377-387 ◽  
Author(s):  
A P Halestrap
Keyword(s):  
Mitochondrial Membrane ◽  
Ketone Body ◽  
Ketone Bodies ◽  
Ph Dependence ◽  
Physiological Regulation ◽  
First Order Kinetics ◽  
Sh Group ◽  
Km Value ◽  
The Difference

The effects of exchangeable ions and pH on the efflux of pyruvate from preloaded mitochondria are reported. Efflux obeys first-order kinetics, and the stimulation of efflux by exchangeable ions such as acetoacetate and lactate obeys Michaelis–Menten kinetics. The apparent Km value +/- S.E. for acetoacetate was 0.56 +/- 0.14 mM (n = 5) and that for lactate 12.3 +/- 2.3 mM (n = 6). The Vmax. values +/- S.E. at 0 degrees C were 16.2 +/- 2.0 and 21.9 +/- 2.7 nmol/min per mg of protein. The exchange of a variety of other substituted monocarboxylates was also studied. Efflux was also stimulated by increasing the external pH. The data gave a pK for the transport process of 8.35 and a Vmax. of 3.31 +/- 0.14 nmol/min per mg. The similarity of the Vmax. values for various exchangeable ions but the difference of this from the Vmax. in the absence of exchangeable ions may indicate that transport of pyruvate occurs with H+ and not in exchange for an OH- ion. The inhibition of transport by alpha-cyano-4-hydroxycinnamate took several seconds to reach completion at 0 degrees C. It is proposed that inhibition occurs by binding to the substrate site and subsequent reaction with an -SH group on the inside of the membrane. The inhibitor can be displaced by substrates that can also enter the mitochondria independently of the carrier and so compete with the inhibitor for the substrate-binding site on the inside of the membrane. A mechanism for transport is proposed that invokes a transition state of pyruvate involving addition of an -SH group to the 2-carbon of pyruvate. Evidence is presented that suggests that ketone bodies may cross the mitochondrial membrane either on the carrier or by free diffusion. The physiological involvement of the carrier in ketone-body metabolism is discussed. The role of ketone bodies and pH in the physiological regulation of pyruvate transport is considered.

scholarly journals Stability of carotenoids toward UV-irradiation in hexane solution

2008 ◽  
Vol 73 (1) ◽  
pp. 15-27 ◽  
Author(s):  
Dragan Cvetkovic ◽  
Dejan Markovic
Keyword(s):  
Free Radical ◽  
Uv Irradiation ◽  
First Order ◽  
Chemical Structures ◽  
First Order Kinetics ◽  
Uv C ◽  
Hexane Solution

The stabilities of four selected carotenoids dissolved in hexane, two carotenes and two xanthophylls, toward UV-irradiation of three different ranges (UV-A, UV-B and UV-C) were studied in this work. The carotenoids underwent bleaching via a probable free radical mediated mechanism following first-order kinetics. The bleaching rates were highly dependent on the input of the involved photons and, although not consistently, on the chemical structures of the investigated compounds. For the two xanthophylls, a possible role of oxygen associated with their bleaching cannot be neglected.

scholarly journals Quantitative analysis of proton-linked transport system. β-Galactoside exit in Escherichia coli

1980 ◽  
Vol 188 (2) ◽  
pp. 467-473 ◽  
Author(s):  
I R Booth ◽  
W A Hamilton
Keyword(s):  
Escherichia Coli ◽  
Quantitative Analysis ◽  
Transport System ◽  
Rate Constants ◽  
The Other ◽  
First Order ◽  
First Order Kinetics ◽  
Solute Accumulation ◽  
External Ph

The exit of lactose and thiomethyl-beta-D-galactoside from Escherichia coli ML308-225 has been studied to determine the role of carrier-dependent (zero-trans efflux) and carrier-independent (leak) processes. On the basis of its sensitivity to p-chloromercuribenzene sulphonate the exit of lactose was found to be almost wholly mediated by the carrier. Consistent with this conclusion was the finding that the rate of exit of this sugar was dependent on the external pH, being considerably slower at acid pH. On the other hand exit of thiomethyl-beta-D-galactoside was found to be composed of both carrier-dependent and carrier-independent processes. Both processes exhibited first-order kinetics with the rate constants for zero-trans efflux and leak being 0.137 min-1 and 0.079 min-1, respectively. The relevance of these findings for out earlier proposal for the methods of attenuation of solute accumulation is discussed [Booth, Mitchell & Hamilton (1979) Biochem. J. 182, 687–696].

Investigations into the role of sulfhydryl groups in the mechanism of action of the nitrates

1982 ◽  
Vol 60 (10) ◽  
pp. 1261-1266 ◽  
Author(s):  
J. A. Moffat ◽  
P. W. Armstrong ◽  
G. S. Marks
Keyword(s):  
Smooth Muscle ◽  
Vascular Smooth Muscle ◽  
Mechanism Of Action ◽  
Active Site ◽  
Sulfhydryl Reagents ◽  
Response Curves ◽  
Sh Groups ◽  
Nitrobenzoic Acid ◽  
Sh Group

The mechanism by which nitroglycerin (GTN) initiates relaxation in vascular smooth muscle is not known. According to one hypothesis a specific nitrate receptor exists with a key sulfhydryl (SH) group in the active site. The current study was performed with sulfhydryl reagents in helical strips of the canine medial saphenous vein from 20 dogs to examine the role of the SH group in the action of GTN. The reagents used were 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB) and p-chloromercuribenzoate (PCMB) which bind to and inactivate SH groups, and dithiothreitol (DTT), an SH reducing agent. It was anticipated that DTNB and PCMB would decrease the sensitivity to GTN while DTT might increase the sensitivity to GTN. Treatment of strips with PCMB and DTNB did not alter the dose–response curves for GTN. In contrast, following DTT treatment (1 × 10−4 M) the maximum response to GTN (10−5 M) was significantly reduced from 80.3% ± 4.0 (SD) in control strips to 46.9% ± 4.4 (SD) in the treated strips. These data suggest that relaxation induced by GTN in vascular smooth muscle occurs by a mechanism other than interaction with membrane SH groups.

Role of pH on Metribuzin Dissipation in Field Soils

Weed Science ◽  
1976 ◽  
Vol 24 (5) ◽  
pp. 508-511 ◽  
Author(s):  
James S. Ladlie ◽  
William F. Meggitt ◽  
Donald Penner
Keyword(s):  
Soil Ph ◽  
Half Life ◽  
Residue Analysis ◽  
Soil Samples ◽  
First Order ◽  
First Order Kinetics ◽  
Field Soils ◽  
Pseudo First Order

Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] residue analysis of soil samples showed greater amounts of residue extractable at soil pH 6.7 than 4.6. Metribuzin leaching increased with increasing soil pH. Metribuzin disappearance from soil followed pseudo first-order kinetics. The half-life of metribuzin decreased as soil pH increased and increased at all soil pH levels as depth of sampling increased. The decreased activity and decreased rate of metribuzin dissipation at lower soil pH is apparently due to protonation and increased adsorption.

scholarly journals Exploring the scope of DBU-promoted amidations of 7-methoxycarbonylpterin

2020 ◽  
Vol 16 ◽  
pp. 509-514 ◽  
Author(s):  
Anna R Bockman ◽  
Jeffrey M Pruet
Keyword(s):  
Reaction Kinetics ◽  
Structural Features ◽  
Product Formation ◽  
Reaction Conditions ◽  
First Order ◽  
First Order Kinetics ◽  
Synthetic Utility ◽  
Pseudo First Order ◽  
Pteridine Derivatives

The synthetic utility of pterins is often hampered by the notorious insolubility of this heterocycle, slowing the development of medicinally relevant pteridine derivatives. Reactions which expedite the development of new pterins are thus of great importance. Through a dual role of diazabicycloundecene (DBU), 7-carboxymethylpterin is converted to the soluble DBU salt, with additional DBU promoting an ester-to-amide transformation. We have explored this reaction to assess its scope and identify structural features in the amines which significantly affect success, monitored the reaction kinetics using a pseudo-first order kinetics model, and further adapted the reaction conditions to allow for product formation in as little as 5 min, with yields often >80%.

scholarly journals The Hsc70 disaggregation machinery removes monomer units directly from α-synuclein fibril ends

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Matthias M. Schneider ◽  
Saurabh Gautam ◽  
Therese W. Herling ◽  
Ewa Andrzejewska ◽  
Georg Krainer ◽  
...  
Keyword(s):  
Molecular Chaperones ◽  
De Novo ◽  
Cellular Protein ◽  
Amyloid Formation ◽  
First Order ◽  
Hsp70 Family ◽  
First Order Kinetics ◽  
Reaction Proceeds ◽  
Kinetics Of

AbstractMolecular chaperones contribute to the maintenance of cellular protein homoeostasis through assisting de novo protein folding and preventing amyloid formation. Chaperones of the Hsp70 family can further disaggregate otherwise irreversible aggregate species such as α-synuclein fibrils, which accumulate in Parkinson’s disease. However, the mechanisms and kinetics of this key functionality are only partially understood. Here, we combine microfluidic measurements with chemical kinetics to study α-synuclein disaggregation. We show that Hsc70 together with its co-chaperones DnaJB1 and Apg2 can completely reverse α-synuclein aggregation back to its soluble monomeric state. This reaction proceeds through first-order kinetics where monomer units are removed directly from the fibril ends with little contribution from intermediate fibril fragmentation steps. These findings extend our mechanistic understanding of the role of chaperones in the suppression of amyloid proliferation and in aggregate clearance, and inform on possibilities and limitations of this strategy in the development of therapeutics against synucleinopathies.

Potassium and Rubidium Effluxes in Saccharomyces cerevisiae

1985 ◽  
Vol 40 (9-10) ◽  
pp. 721-725 ◽  
Author(s):  
María D . Ortega ◽  
Alonso Rodríguez-Navarro
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Ph Regulation ◽  
Uptake System ◽  
Acidic Ph ◽  
Efflux System ◽  
First Order ◽  
Ph Values ◽  
First Order Kinetics

Abstract In growing cells, K+ and Rb+ effluxes followed first order kinetics, took place with slight differences between K+ and Rb+ and were stimulated at acidic pH values. In uncoupled cells and ATP-depleted cells, K+ efflux was higher than Rb+ efflux. In ATP-depleted cells, the effluxes were not stimulated at acidic pH values. Two different K+ effluxes are proposed: (i) the normal efflux, which may be a K+/H+ antiport and does not function in ATP-depleted cells, and (ii) the backward reaction of the uptake system, which can be high in depolarized cells. The role of the normal efflux system in K+ content and pH regulation is discussed.

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