scholarly journals Temperature and enzyme activity in poikilotherms. Isocitrate dehydrogenases in rainbow-trout liver

1971 ◽  
Vol 123 (5) ◽  
pp. 695-705 ◽  
Author(s):  
Thomas W. Moon ◽  
P. W. Hochachka
Keyword(s):  
Enzyme Activity ◽  
Rainbow Trout ◽  
Isocitrate Dehydrogenase ◽  
Low Temperatures ◽  
Substrate Affinity ◽  
Thermally Induced ◽  
Cold Adapted ◽  
Enzyme Substrate ◽  
Kinetics Of ◽  
Rainbow Trout Liver

1. The kinetics of the thermally induced enzyme variants of the supernatant NADP–isocitrate dehydrogenase from rainbow-trout liver are investigated. 2. Fish acclimatized to 2°C (cold-adapted enzyme) and 17°C (warm-adapted enzyme) show different relative distributions of the three NADP–isocitrate dehydrogenase isoenzymes; this has been demonstrated with electrophoresis and electrofocusing techniques. 3. Plots of Km versus temperature for the cold-adapted and warm-adapted enzyme variants are complex in nature with apparent maximal enzyme–substrate affinity corresponding to the temperature at which the trout is acclimatized. Both substrates, dl-isocitrate and NADP+, give similar curves although the magnitude of the Km change with temperature is much decreased in the case of NADP+. 4. Ea values of approx. 18kcal/mol were determined for both the cold-adapted and warm-adapted enzyme variants. 5. In an attempt to determine how velocities can be increased at low temperatures, cation, pH requirements, metabolite and enzyme concentrations were examined. 6. NAD–isocitrate dehydrogenase could not be detected in trout tissues.

scholarly journals The effect of pH on the kinetics of arylsulphatases A and B

1983 ◽  
Vol 213 (3) ◽  
pp. 603-607 ◽  
Author(s):  
C O'Fagain ◽  
B M Butler ◽  
T J Mantle
Keyword(s):  
Enzyme Activity ◽  
Rat Liver ◽  
Substrate Binding ◽  
Acid Base ◽  
Effect Of Ph ◽  
Substrate Complex ◽  
Enzyme Substrate ◽  
General Acid ◽  
Kinetics Of

The effect of pH on the kinetics of rat liver arylsulphatases A and B is very similar and shows that two groups with pK values of 4.4-4.5 and 5.7-5.8 are important for enzyme activity. Substrate binding has no effect on the group with a pK of 4.4-4.5; however, the pK of the second group is shifted to 7.1-7.5 in the enzyme-substrate complex. An analysis of the effect of pH on the Ki for sulphate inhibition suggests that HSO4-is the true product. A model is proposed that involves the two ionizing groups identified in the present study in a concerted general acid-base-catalysed mechanism.

A new cold-adapted serine peptidase from Antarctic Lysobacter sp. A03: Insights about enzyme activity at low temperatures

2017 ◽  
Vol 103 ◽  
pp. 854-862 ◽  
Author(s):  
Jamile Queiroz Pereira ◽  
Adriana Ambrosini ◽  
Luciane Maria Pereira Passaglia ◽  
Adriano Brandelli
Keyword(s):  
Enzyme Activity ◽  
Low Temperatures ◽  
Cold Adapted ◽  
Serine Peptidase

scholarly journals Patterns of apparent co-operativity in a simple random non-equilibrium enzyme–substrate–modifier mechanism. Comparison with equilibrium allosteric models

1979 ◽  
Vol 177 (2) ◽  
pp. 631-639 ◽  
Author(s):  
Edward P. Whitehead ◽  
Maarten R. Egmond
Keyword(s):  
Steady State ◽  
Substrate Affinity ◽  
State Equations ◽  
Allosteric Interactions ◽  
Enzyme Substrate ◽  
Steady State Kinetics ◽  
Family Of Curves ◽  
The Family ◽  
Kinetics Of ◽  
Non Equilibrium

It has often been claimed that random non-equilibrium mechanisms can result in apparent homotropic and heterotropic effects in steady-state kinetics of the kind more usually attributed to intersubunit allosteric interactions. However, it has never been shown whether any simple random mechanism could in fact give patterns of apparent interaction similar to those predicted by the well-known allosteric models. The patterns of apparent substrate co-operativity and affinity given by the steady-state of a standard simple random substrate–modifier mechanism in which catalytic velocity is proportional to substrate binding have been analysed mathematically and numerically. All patterns possible with this model are described. Some of them rather resemble those possible with standard allosteric models, in that there is a high-affinity and a low-affinity form at zero and infinite modifier concentrations (or vice versa) which show Michaelian behaviour, apparent co-operativity passing through a maximum or minimum at intermediate affinities. Unlike the allosteric models the family of curves is in principle not symmetrical. The random model can also give behaviour not possible with the standard allosteric models, such as higher substrate affinity at intermediate modifier concentrations than at either zero or infinite modifier, with concomitant negative apparent substrate co-operativity, or a single change of sign of apparent substrate co-operativity. The analysis uses recently discovered simplified forms of steady-state equations for random models.

scholarly journals Inactivation kinetics of dihydrofolate reductase from Chinese hamster during urea denaturation

1997 ◽  
Vol 324 (2) ◽  
pp. 395-401 ◽  
Author(s):  
Jia-Wei WU ◽  
Zhi-Xin WANG ◽  
Jun-Mei ZHOU
Keyword(s):  
Enzyme Activity ◽  
Dihydrofolate Reductase ◽  
Single Phase ◽  
Tertiary Structure ◽  
Chinese Hamster ◽  
Free Enzyme ◽  
Inactivation Kinetics ◽  
Binary And Ternary Complexes ◽  
Enzyme Substrate ◽  
Kinetics Of

The kinetic theory of substrate reaction during modification of enzyme activity has been applied to the study of inactivation kinetics of Chinese hamster dihydrofolate reductase by urea [Tsou (1988) Adv. Enzymol. Relat. Areas Mol. Biol. 61, 381–436]. On the basis of the kinetic equation of substrate reaction in the presence of urea, all microscopic kinetic constants for the free enzyme and enzyme–substrate binary and ternary complexes have been determined. The results of the present study indicate that the denaturation of dihydrofolate reductase by urea follows single-phase kinetics, and changes in enzyme activity and tertiary structure proceed simultaneously in the unfolding process. Both substrates, NADPH and 7,8-dihydrofolate, protect dihydrofolate reductase against inactivation, and enzyme–substrate complexes lose their activity less rapidly than the free enzyme.

Effect of the hydrophilicity of the polymer matrix on immobilized α-chymotrypsin

1984 ◽  
Vol 49 (6) ◽  
pp. 1552-1556
Author(s):  
Minoru Kumakura ◽  
Isso Kaetsu
Keyword(s):  
Thermal Stability ◽  
Enzyme Activity ◽  
Pore Size ◽  
Polymer Matrix ◽  
Low Temperatures ◽  
Radiation Polymerization ◽  
Thermal Stability Of

α-Chymotrypsin was immobilized by radiation polymerization at low temperatures and the effect of the hydrophilicity of the polymer matrix on the enzyme activity and thermal stability was studied. The activity and thermal stability of immobilized chymotrypsin increased with the increasing hydrophilicity of the polymer matrix or monomer. The thermal stability was affected by the form and pore size of the polymer matrix; chymotrypsin immobilized on a soft-gel polymer matrix exhibited an enhanced thermal stability.

Uptake of taurocholic acid and cholic acid in isolated hepatocytes from rainbow trout

1994 ◽  
Vol 267 (3) ◽  
pp. G380-G386 ◽  
Author(s):  
C. M. Rabergh ◽  
K. Ziegler ◽  
B. Isomaa ◽  
M. M. Lipsky ◽  
J. E. Eriksson
Keyword(s):  
Rainbow Trout ◽  
Bile Acids ◽  
Low Temperatures ◽  
High Efficiency ◽  
Isolated Hepatocytes ◽  
Metabolic Inhibitors ◽  
Dependent Manner ◽  
Rainbow Trout Oncorhynchus Mykiss ◽  
Transport Component ◽  
Efficient Uptake

The uptake of the bile acids cholate (CHA) and taurocholate (TCHA) was studied in isolated hepatocytes from rainbow trout (Oncorhynchus mykiss). Both CHA and TCHA were taken up in a concentration- and temperature-dependent manner with optimum temperature at 15 degrees C and a strikingly efficient uptake even at low temperatures (0-5 degrees C). The total uptake was a combination of a saturable [Michaelis-Menten constant (Km) for CHA, 20 microM; Km for TCHA, 19 microM] and a nonsaturable component. The maximal uptake rate of the saturable component was 416 and 805 pmol.mg protein-1.min-1 for CHA and TCHA, respectively. The uptake of both bile acids was shown to be energy dependent, since it was inhibited by the metabolic inhibitors antimycin A, oligomycin and carbonyl cyanide m-chlorophenylhydrazone. The uptake was clearly Na+ independent, since isosmotic replacement of extracellular Na+ by Li+, choline, or K+ did not inhibit the uptake. Furthermore, it seemed to be independent of the presence of extracellular Cl-, since it was not inhibited by replacement of Cl- with sodium gluconate. On the whole, our results show that the hepatocellular uptake of bile acids in rainbow trout is mediated by a Na(+)-independent carrier system, with characteristics resembling the corresponding transport component in mammalian hepatocytes, but with high efficiency even at low temperatures.

Kinetics of the Thermally-Induced Structural Rearrangement of γ-MnO2

2014 ◽  
Vol 118 (42) ◽  
pp. 24257-24265 ◽  
Author(s):  
Wesley M. Dose ◽  
Neeraj Sharma ◽  
Nathan A. S. Webster ◽  
Vanessa K. Peterson ◽  
Scott W. Donne
Keyword(s):  
Structural Rearrangement ◽  
Thermally Induced ◽  
Kinetics Of
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