scholarly journals Temperature and the regulation of enzyme activity in poikilotherms. Properties of rainbow-trout fructose diphosphatase

1969 ◽  
Vol 111 (3) ◽  
pp. 287-295 ◽  
Author(s):  
H. W. Behrisch ◽  
P. W. Hochachka
Keyword(s):  
Enzyme Activity ◽  
Rainbow Trout ◽  
Temperature Adaptation ◽  
Temperature Dependent ◽  
Ph Optimum ◽  
Physiological Temperature ◽  
Low Concentrations ◽  
High Concentrations ◽  
Regulation Of Enzyme Activity ◽  
Hill Plots

1. The properties of fructose diphosphatase from the liver of rainbow trout (Salmo gairdnerii) were examined over the physiological temperature range of the organism. 2. Saturation curves for substrate (fructose 1,6-diphosphate) and a cofactor (Mg2+) are sigmoidal, and Hill plots of the results suggest a minimum of two interacting fructose 1,6-diphosphate sites and two interacting Mg2+ sites per molecule of enzyme. 3. Mn2+-saturation curves are hyperbolic, and the Ka for Mn2+, which inhibits the enzyme at high concentrations, is 50–100-fold lower than the Ka for Mg2+. 4. Fructose diphosphatase is inhibited by low concentrations of AMP; this inhibition appears to be decreased and reversed by increasing the concentrations of Mg2+ and Mn2+. Higher concentrations of AMP are required to inhibit the trout fructose diphosphatase in the presence of Mn2+. 5. The affinities of fructose diphosphatase for fructose diphosphate and Mn2+ appear to be temperature-independent, whereas the affinities for Mg2+ and AMP are highly temperature-dependent. 6. The pH optimum of the enzyme depends on the concentrations of Mg2+ and Mn2+. In addition, pH determines the Ka for Mg2+; at high pH, Ka for Mg2+ is lowered. 7. The enzyme is inhibited by Ca2+ and Zn2+, and the inhibition is competitive with respect to both cations. 8. The possible roles of these ions and AMP in the modulation of fructose diphosphatase and gluconeogenic activity are discussed in relation to temperature adaptation.

scholarly journals Temperature and the regulation of enzyme activity in poikilotherms. Properties of lungfish fructose diphosphatase

1969 ◽  
Vol 112 (5) ◽  
pp. 601-607 ◽  
Author(s):  
Hans Werner Behrisch ◽  
Peter W. Hochachka
Keyword(s):  
Enzyme Activity ◽  
Temperature Adaptation ◽  
South American ◽  
Ph Optimum ◽  
Low Concentrations ◽  
Positive Modulator ◽  
Regulation Of Enzyme Activity ◽  
Hill Plots

1. The properties of fructose diphosphatase from liver of South American lungfish (Lepidosiren paradoxa) were examined. 2. Saturation curves for substrate (fructose diphosphate) and both cofactors (Mn2+ and Mg2+) are sigmoidal and Hill plots of these results suggest about 2 interacting substrate and cofactor sites/molecule of enzyme. 3. Mn2+ is an efficient positive modulator of the enzyme and Ka for Mn2+ is about 20–30-fold lower than the Ka for Mg2+. 4. Lungfish fructose diphosphatase is inhibited by low concentrations of AMP, and the affinity of the enzyme for AMP is insensitive to temperature. 5. The affinities of fructose diphosphatase for fructose diphosphate and Mn2+ appear to be dependent on temperature, whereas affinity for Mg2+ is temperature-independent. 6. The pH optimum of the enzyme depends on the presence of the particular cofactor. As pH increases, the Ka values of both cations are lowered, maximum velocities are increased and the saturation curves for cofactor become hyperbolic. 7. The possible roles of these ions, pH and substrate in the modulation of fructose diphosphatase and gluconeogenic activity in the lungfish are discussed in relation to aestivation and temperature adaptation.

Copper, nickel, and thallium uptake by the lichen Cladina rangiferina

1981 ◽  
Vol 59 (1) ◽  
pp. 91-100 ◽  
Author(s):  
M. A. S. Burton ◽  
P. LeSueur ◽  
K. J. Puckett
Keyword(s):  
Metal Uptake ◽  
Deionized Water ◽  
Metabolic Inhibitors ◽  
Temperature Dependent ◽  
Low Concentrations ◽  
Nickel Uptake ◽  
High Concentrations ◽  
Uptake Studies ◽  
Cladina Rangiferina ◽  
Very High

Metal uptake studies with Cladina rangiferina showed that the affinity for nickel was much lower than for copper or thallium. Nickel uptake was not decreased by the absence of light or oxygen or by pretreatment with metabolic inhibitors. Nickel uptake was not temperature dependent but was very dependent upon pH.Cation-exchange studies demonstrated that there was a stoichiometric exchange of Ni2+ for Sr2+, and Cu2+ for Sr2+. The exchange of Tl+ for Sr2+ was not stoichiometric, excess Tl+ was accumulated in relation to the Sr2+ released. The ratio of Sr2+:Tl+ exchange increased with increasing Tl+ availability from 1:9 (12.5 μmol Tl+ available/g of lichen) to 1:2 (500 μmol Tl+ available). Acid-treated lichen gave the expected exchange ratio of 1:2. Washing of the thalli with deionized water resulted in the continued loss of Tl+ from acid-treated and live C. rangiferina. Copper and nickel were not released in this manner.Increasing concentrations of copper and thallium produced a corresponding loss of potassium from the thallus. The potassium loss was initiated at low concentrations of copper and thallium whereas very high concentrations of manganese and nickel were required to bring about the same response.

The Regulation of Acetyl Coenzyme A Synthesis in Chloroplasts

1985 ◽  
Vol 40 (7-8) ◽  
pp. 496-502 ◽  
Author(s):  
Hans-Jürgen Treede ◽  
Klaus-Peter Heise
Keyword(s):  
Pyruvate Dehydrogenase Complex ◽  
Acetyl Coa ◽  
Ph Optimum ◽  
Spinach Chloroplasts ◽  
Branched Chain Amino Acid ◽  
Pea Seedlings ◽  
Low Concentrations ◽  
Acetyl Coa Synthesis ◽  
High Concentrations ◽  
Branched Chain

Abstract The enzymatic activities of the pyruvate dehydrogenase complex (PDC) and acetyl-CoA synthetase (ACS) have been compared in extracts of plastids isolated from spinach leaves and from both green and etiolated pea seedlings. A ll plastid preparations were shown to be capable of synthesizing acetyl-CoA, not only via acetyl-CoA synthetase, but also via the pyruvate dehydroge­ nase complex, though, with different activities. Both pathways are apparently under metabolic control. Thus, the substrate levels in photosynthetically active spinach chloroplasts appear to favor acetyl-CoA synthesis via ACS (apparent Km for acetate of 0.1 mм) , because calculated stromal pyruvate levels (0.1 m M) appear to limit its formation via the PDC (apparent Km for pyruvate of 0.2-0.3 nм) . In spinach chloroplasts, therefore, the PDC pathway seems to be predominantly involved in providing precursors for branched-chain amino acid biosynthesis (vali­ne, leucine and isoleucine). Acetyl-CoA, synthesized via ACS, may additionally function as an inhibitor of the chloroplast PD C , because, as in mitochondria, relatively low concentrations of the end products NADH and acetyl-CoA strongly inhibit the PD C in chloroplast extracts. On the other hand, comparatively high concentrations of MgATP, a cofactor for ACS, inhibited the PDC complex. The pH optimum of about 8 and the high Mg-requirement distinguishes both enzymes from mitochondrial PDC and reflects an accomodation to stromal conditions in photosynthetically active chloroplasts.

A carrier-mediated system for transport of biotin in rat intestine in vitro

1987 ◽  
Vol 252 (1) ◽  
pp. G52-G55 ◽  
Author(s):  
H. M. Said ◽  
R. Redha
Keyword(s):  
Methyl Ester ◽  
Temperature Dependent ◽  
Rat Intestine ◽  
Simple Diffusion ◽  
Low Concentrations ◽  
Structural Analogues ◽  
High Concentrations ◽  
Biotin Molecule ◽  
Energy Dependent

Transport of biotin was examined in rat intestine using the everted sac technique. Transport of 0.1 microM biotin was linear with time for at least 30 min of incubation and occurred at a rate of 3.7 pmol X g initial tissue wet wt-1 X min-1. Transport of biotin was higher in the jejunum than the ileum and was minimum in the colon (85 +/- 6, 36 +/- 6, and 2.8 +/- 0.6 pmol X g initial tissue wet wt-1 X 25 min-1, respectively). In the jejunum, transport of biotin was saturable at low concentrations (Kt = 3.73, microM, Vmax = 3.11 nmol X g initial tissue wet wt-1 X 25 min-1) but linear at higher concentrations (greater than 10 microM). The transport of low concentrations of biotin was inhibited by structural analogues (desthiobiotin, biotin methyl ester, diaminobiotin, and biocytin), Na+ dependent, energy dependent, temperature dependent, and proceeded against a concentration gradient in the serosal compartment. No metabolic alteration occurs to the biotin molecule during transport. This study demonstrates that biotin transport in rat intestine occurs by a carrier-mediated process at low concentrations and by simple diffusion at high concentrations. Furthermore, the carrier-mediated process is Na+, energy, and temperature dependent.

scholarly journals The effects of the tylosin and Cd on soil enzyme activity

2020 ◽  
Vol 213 ◽  
pp. 01032
Author(s):  
Zhaohong Meng ◽  
Shuman Wang ◽  
Jia Zhou
Keyword(s):  
Heavy Metals ◽  
Enzyme Activity ◽  
Soil Enzyme ◽  
Soil Enzyme Activity ◽  
Germination Index ◽  
Soil Microbial ◽  
Low Concentrations ◽  
Long Time ◽  
High Concentrations ◽  
Microbial Environment

Soil microbial environment have been affected by different concentration heavy metals Cd (HM) and tylosin (TYL) and combination of TYL and HM interactions. Degradation of TYL was caused certain inhibition due to the addition of HM. The germination index of seed had been inhibited owing to the toxic effects of HM and TYL, but we found that the low concentrations of HM (4 mg/kg), the germination index higher than the soil which unadded HM and TYL in it. The soil enzyme activity was significantly suppressed by the addition of HM and TYL. Actinomycete was inhibited by high concentrations of HM for a long time. The studies demonstrated that the pollution of the soil micro-environment has been serious than only add HM or TYL in the soil.

Characteristics of spermidine uptake by isolated rat enterocytes

1989 ◽  
Vol 256 (5) ◽  
pp. G905-G910 ◽  
Author(s):  
J. Kumagai ◽  
R. Jain ◽  
L. R. Johnson
Keyword(s):  
Temperature Dependent ◽  
New Synthesis ◽  
Low Concentrations ◽  
Carrier Mechanism ◽  
Electrical Gradient ◽  
High Concentrations ◽  
The One ◽  
Energy Dependent ◽  
Rat Enterocytes ◽  
Isolated Rat

Eukaryotic cells require polyamines for growth. The supply of polyamines to growing cells may be increased either by new synthesis or increased uptake. We have recently shown that putrescine uptake by isolated rat enterocytes is energy dependent, saturable, and ouabain insensitive. Although putrescine uptake was inhibited by putrescine and cadaverine, it was not inhibited by equal concentrations of spermine and spermidine. These data indicated that a carrier mechanism separate from that putrescine existed for spermidine and spermine. In the current study spermidine uptake by isolated enterocytes was saturable, temperature dependent, and inhibited by 1 mM KCN. Kinetic analysis resulted in a Km = 2.51 x 10(-6) M and a Vmax = 3.57 x 10(-12) mol.10(6) cells-1.15 min-1. Spermidine uptake was 70% inhibited by 1 mM ouabain. Replacement of sodium by choline, lithium, tetramethylammonium, or N-methyl-D-glucamine also inhibited spermidine uptake. Replacement of Na+ by mannitol or sucrose, however, depressed uptake but not significantly. Spermidine uptake was inhibited by 1 mM ouabain. Spermidine uptake was inhibited by relatively low concentrations of spermine and high concentrations of putrescine; while putrescine uptake was inhibited by relatively high concentrations of both spermine and spermidine. Kinetic data indicated that spermidine and spermine share a carrier that is distinct from the one mediating the uptake of putrescine. While spermidine uptake does not appear to depend on Na+ cotransport, it may be dependent on the electrical gradient established by the Na+-K+-ATPase.

Influence of thiol substances on in vitro and in vivoL-thyroxine deiodination in rainbow trout, Salmo gairdneri

1984 ◽  
Vol 62 (8) ◽  
pp. 1495-1501 ◽  
Author(s):  
J. G. Eales ◽  
Shirley Shostak ◽  
Catherine G. Flood
Keyword(s):  
Rainbow Trout ◽  
Reduced Glutathione ◽  
Salmo Gairdneri ◽  
Physiological Conditions ◽  
Low Concentrations ◽  
Dtt Dithiothreitol ◽  
High Concentrations ◽  
Stimulation Of

The effects of the thiols DTT (dithiothreitol) and GSH (reduced glutathione) on hepatic in vitro and in vivo T4 (L-thyroxine) deiodination by rainbow trout held at 11 °C were studied. Hepatic deiodination increased progressively over the DTT range of 0.02–20 mM. GSH was less potent than DTT at low concentrations and strongly inhibited deiodination at high concentrations (> 1 mM). Hepatic deiodination was not increased by 1 mM NADPH or anaerobic conditions and was enhanced and not inhibited by the GSH inhibitor, diamide (2.5 mM), indicating that the low T4 deiodination in the absence of DTT is not due to endogenous GSH deficiency. Intraperitoneally injected GSH consistently increased plasma levels of 125I and [125I]-3,5,3′-triiodo-L-thyronine (T3) in fed or starved [125I]T4-injected trout, suggesting a GSH stimulation of extrahepatic T4 deiodination. However, injected GSH did not elevate plasma T3 concentrations. This was probably due to a demonstrated GSH stimulation of plasma T4 and T3 clearance. Force-fed GSH did not increase [125I]T4 deiodination. It is concluded that exogenous thiols can enhance T4 deiodination both in vitro and in vivo. However, availability of neither endogenous nor dietary GSH appears to regulate T4 deiodination under physiological conditions, including altered nutritional state.

scholarly journals Purification and some properties of 1-aspartamido-β-N-acetylglucosamine amidohydrolase from human liver

1977 ◽  
Vol 165 (3) ◽  
pp. 497-502 ◽  
Author(s):  
B Dugal ◽  
J Strømme
Keyword(s):  
Enzyme Activity ◽  
Human Liver ◽  
Disc Electrophoresis ◽  
Temperature Dependent ◽  
Ph Optimum ◽  
Total Enzyme Activity ◽  
Bivalent Ions ◽  
Apparent Homogeneity ◽  
Km Value ◽  
Total Enzyme

Human liver 1-aspartamido-beta-N-acetylglucosamine amidohydrolase (aspartylglucosylaminase, EC 3.5.1.26) was purified 17 500-fold to apparent homogeneity as judged from polyacrylamide-gel disc electrophoresis. A pH optimum of 7.7-9.0 was found. The Km value was pH- and temperature-dependent. At 37 degrees C and pH 7.7, Km was 0.16 mM and it increased to 0.29 at pH 6.0 and 0.23 at pH 9.0. At 25 degrees C and pH 7.7, a Km value of 0.99 mM was obtained. When the substrate concentration was varied, apparent Michaelis-Menten kinetics were obtained. p-Hydroxymercuribenzoate, glutathione or cysteine had no effect on the enzyme activity; 5 mM-N-acetylcysteine inhibited about 47% of the total enzyme activity. Apart from Cu2+, other bivalent ions were virtually ineffective at 1 mM. The kinetic study differentiates this enzyme from aspartylglucosylaminase from other sources.

Effects of amino acids on Thiobacillus acidophilus. II. Threonine deaminase

1980 ◽  
Vol 26 (3) ◽  
pp. 385-388 ◽  
Author(s):  
Gérald Proteau ◽  
Marvin Silver
Keyword(s):  
Amino Acids ◽  
Enzyme Activity ◽  
Ammonium Sulfate ◽  
Active Site ◽  
Binding Sites ◽  
Threonine Deaminase ◽  
Low Concentrations ◽  
High Concentrations ◽  
Thiobacillus Acidophilus ◽  
Optimal Ph

Biosynthetic L-threonine deaminase was partially purified 73-fold with a 60% recovery from Thiobacillus acidophilus by ammonium sulfate fractionation and by Sepharose 6B-C1 chromatography. The optimal pH for enzyme activity was between 9.0 and 10.0 and no optimal pH shift was observed in the presence of L-isoleucine, an inhibitor. The enzyme was effectively inhibited by L-isoleucine and showed homotropic interaction only in the presence of L-isoleucine.Kinetic studies indicate that there are at least two threonine binding sites and at least two isoleucine binding sites. The Km for threonine is 2.5 × 10−3 M. The inhibition due to isoleucine is reversed by low concentrations of L-valine. L-Valine at high concentrations acts as a substrate analogue and competitively inhibits L-threonine binding at the active site; the K1 is 1.6 × 10−2 M.

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