scholarly journals Temperature and the regulation of enzyme activity in poikilotherms. Regulatory properties of fructose diphosphatase from muscle of the Alaskan king-crab

1971 ◽  
Vol 121 (3) ◽  
pp. 399-409 ◽  
Author(s):  
Hans W. Behrisch
Keyword(s):  
Skeletal Muscle ◽  
Enzyme Activity ◽  
Low Temperature ◽  
Temperature Sensitive ◽  
King Crab ◽  
Rate Limiting Step ◽  
Low Concentrations ◽  
Higher Temperature ◽  
Paralithodes Camtschatica ◽  
Rate Limiting

1. The properties of fructose diphosphatase from skeletal muscle of the Alaskan king-crab (Paralithodes camtschatica) were examined over the physiological temperature range of the animal. 2. King-crab muscle fructose diphosphatase is first activated by Na+ and NH4+ and is then partially inhibited by these cations at concentrations higher than 10mm at 0°, 8° and 15°C. Enzyme activity is stimulated by K+ at 0°C, but is curtailed at 8°C and 15°C, an effect that could render rate independent of temperature. 3. Affinity for substrate increases with decreasing temperature; below the temperature of acclimatization, Km for fructose 1,6-diphosphate increases, resulting in a complex U-shaped temperature–Km curve. 4. King-crab muscle fructose diphosphatase is inhibited by low concentrations of AMP. As with enzymes of other poikilotherms, inhibition by AMP is sensitive to temperature; the enzyme is least sensitive to inhibition by AMP near the temperature of acclimatization. 5. The affinity of fructose diphosphatase for fructose 1,6-diphosphate is enhanced by phosphoenolpyruvate, and this activation is temperature-sensitive; 0.5mm-phosphoenolpyruvate causes a sevenfold decrease in Km for fructose 1,6-diphosphate at 15°C but a 25-fold decrease at 0°C. 6. Phosphoenolpyruvate appears to decrease the affinity of king-crab muscle fructose diphosphatase for AMP at low temperature, whereas at the higher temperature it appears to enhance inhibition by AMP. Phosphoenolpyruvate was not observed to cause a reversal of inhibition of fructose diphosphatase activity by AMP. The identification of phosphoenolpyruvate as an activator of a rate-limiting step in gluconeogenesis permits the suggestion of a coupling of the controlling mechanisms of several steps in the glycolytic and gluconeogenic chains. 7. These findings suggest mechanisms for the maintenance and regulation of control of fructose diphosphatase activity in king-crab skeletal muscle at low temperature and under conditions that favour concomitant activity of phosphofructokinase.

The Deposition of Silicon Oxide Films by LPCVD at Temperatures as Low as 100°C from a New Liquid Source

1992 ◽  
Vol 282 ◽  
Author(s):  
K. Hochberg ◽  
David A. Roberts
Keyword(s):  
Low Temperature ◽  
Silicon Oxide ◽  
Oxide Films ◽  
Temperature Sensitive ◽  
Oxide Layers ◽  
Low Temperature Deposition ◽  
Liquid Source ◽  
Temperature Deposition ◽  
Higher Temperature

ABSTRACTA precursor for the LPCVD of silicon oxide films has been developed that extends the low temperature deposition range to 100°C. The chemical, 1,4 disilabutane (DSB), produces silicon oxide depositions similar to those of the higher temperature silane and diethylsilane (DES) processes. Optimum DSB processes require pressures below 300 mTorr, similar to silane, in contrast to DES pressures above 600 mTorr at 350°C. This results in poorer conformalities than those of DES, but the step coverages are still superior to those from silane oxides. The DSB films are low stress, carbon-free oxide layers that are suitable for temperature-sensitive underlayers and substrates such as photoresist, plastics, GaAs, and HgCdTe.

scholarly journals Control of the flux in the arginine pathway of Neurospora crassa. Modulations of enzyme activity and concentration

1981 ◽  
Vol 200 (2) ◽  
pp. 231-246 ◽  
Author(s):  
H J Flint ◽  
R W Tateson ◽  
I B Barthelmess ◽  
D J Porteous ◽  
W D Donachie ◽  
...  
Keyword(s):  
Enzyme Activity ◽  
Enzyme Activities ◽  
Genetic Recombination ◽  
Quantitative Measure ◽  
Sensitivity Coefficient ◽  
Mass Action ◽  
Rate Limiting Step ◽  
One Step ◽  
Rate Limiting ◽  
Different Parts

The influence of particular enzyme activities on the flux of metabolites in a pathway can be estimated by ‘modulating’ enzymes (i.e. changing turnover or concentration) and measuring the response in various parts of the system. By controlling the nuclear ration of two genetically different nuclear types in heterokaryons, the enzyme concentrations at four different steps in the arginine pathway were decreased over a range. This range was extended by the use of bradytrophs, mutant strains specifying enzymes with greatly diminished enzyme activities. Strains altered simultaneously at more than one step were also constructed by genetic recombination. By measuring the outputs of the pathway and the steady-state concentrations of intermediate pools, the fluxes in different parts of the pathway were calculated. This allowed the construction of flux/enzyme relationships, the slope of which is a measure of the sensitivity of a flux to the change in enzyme activity at that step. All fluxes were found to be considerably buffered for quite substantial decreases in the activities of all enzymes. Mass action plays an important part in this phenomenon, as do inhibition and repression. Because of the existence of expansion fluxes in growing systems, we find quantitatively different fluxes in different parts of the single pathway. For the same reason some enzyme modulations given decreased fluxes in one part and increased fluxes in another. The understanding of control in the pathway thus involves consideration of many mechanisms operating simultaneously and the estimation of changes in the whole system. The concept of a ‘rate-limiting step’ is found to be inadequate and is replaced by a quantitative measure, the Sensitivity Coefficient, which takes account of all the interactions. It is shown that control of the flux is shared among all the enzymes of the pathway. The results are discussed in terms of the theory of flux control.

scholarly journals New Spectrophotometric Method for the Assessment of Catalase Enzyme Activity in Biological Tissues

2020 ◽  
Vol 16 (8) ◽  
pp. 1054-1062 ◽  
Author(s):  
Thulfeqar A. Hamza ◽  
Mahmoud H. Hadwan
Keyword(s):  
Hydrogen Peroxide ◽  
Enzyme Activity ◽  
Clinical Pathology ◽  
Biological Tissues ◽  
Ammonium Molybdate ◽  
Spectrophotometric Methods ◽  
Rate Limiting Step ◽  
Coefficients Of Variation ◽  
Rate Limiting ◽  
Health Applications

Background: Catalase is a vital antioxidant enzyme that dismutates H2O2 into water and molecular oxygen. Many protocols have been developed to measure catalase enzyme activity. Spectrophotometric methods are the most common assays that used to assess catalase enzyme activity. Methods: Because the rate-limiting step during catalase enzyme activity depends upon the dissociation of hydrogen peroxide, the developed assay measures the reaction between a hydroquinone/ anilinium sulfate/ammonium molybdate reagent and Unreacted Hydrogen Peroxide, which results in the production of a purple, disubstituted quinone compound with a maximum absorbance value at 550 nm. Results: To clarify the precision of the developed method, the coefficients of variation were determined to be 2.6% and 4.7% within run measurements and between run measurements, respectively. This method returned results that correlated well (r = 0.9982) with the results returned using the peroxovanadate method to assess catalase enzyme activity. Additionally, we examined the use of the newly developed hydroquinone assay to measure catalase enzyme activity in liver and bacterial homogenate samples. Conclusion: These results demonstrated that this assay can be used for scientific research and routine health applications because it is inexpensive, simple, accurate, and rapid. This method is suitable for use in clinical pathology laboratories because it is simple and produces precise and reproducible results.

Exogenous application of 5-aminolevulinic acid improves low-temperature stress tolerance of maize seedlings

2018 ◽  
Vol 69 (6) ◽  
pp. 587 ◽  
Author(s):  
Yi Wang ◽  
Jing Li ◽  
Wanrong Gu ◽  
Qian Zhang ◽  
Lixin Tian ◽  
...  
Keyword(s):  
Enzyme Activity ◽  
Low Temperature ◽  
Antioxidant Enzyme ◽  
Temperature Stress ◽  
Aminolevulinic Acid ◽  
Photosynthetic Capacity ◽  
Antioxidant Enzyme Activity ◽  
Low Temperature Stress ◽  
Temperature Sensitive ◽  
Maize Seedlings

The important plant growth regulator 5-aminolevulinic acid (ALA) could promote low-temperature stress tolerance of many plants; however, the underlying mechanisms remain to be elucidated. We investigated the effects of exogenously applied ALA on seedling morphology, antioxidant enzyme activity and photosynthetic capacity of maize (Zea mays L.) seedlings under low-temperature stress. Two cultivars, low-temperature-sensitive cv. Suiyu 13 (SY13) and low-temperature-tolerant cv. Zhengdan 958 (ZD958), were subjected to four treatments: low-temperature without ALA treatment, low-temperature after ALA treatment, normal temperature without ALA treatment, and normal temperature after ALA treatment. Plant morphological growth, proline content, antioxidant enzyme activity and photosynthetic capacity were determined. ALA treatment significantly decreased the inhibitory effects of low-temperature stress on seedling dry weight and increased proline accumulation under low temperatures in ZD958. Pre-application of ALA significantly improved superoxide dismutase and catalase activities in SY13 under low-temperature stress. Furthermore, treating maize seedlings with ALA resulted in significant enhancement of ribulose-1,5-bisphosphate (RuBP) carboxylase activity under low-temperature stress in both cultivars. Pre-treatment with ALA relieved the damage caused by low-temperature stress to maize seedlings, particularly in the low-temperature-sensitive cultivar. Therefore, ALA at appropriate concentrations may be used to prevent reductions in maize crop yield due to low-temperature stress.

Enterohepatic circulation of scymnol sulfate in an elasmobranch, the little skate (Raja erinacea)

1997 ◽  
Vol 273 (5) ◽  
pp. G1023-G1030 ◽  
Author(s):  
Gert Fricker ◽  
Ralph Wössner ◽  
Jürgen Drewe ◽  
Ruth Fricker ◽  
James L. Boyer
Keyword(s):  
Enterohepatic Circulation ◽  
Isolated Hepatocytes ◽  
Hepatic Uptake ◽  
Transport Systems ◽  
Temperature Sensitive ◽  
Hepatic Transport ◽  
Rate Limiting Step ◽  
Direct Demonstration ◽  
Bile Alcohol ◽  
Rate Limiting

The sulfated bile alcohol scymnol sulfate (ScyS), 3α,7α,12α,24ξ,26,27-hexahydroxy-5β-cholestane-26(27)-sulfate, is the major bile salt in bile of an elasmobranch, the little skate. To investigate hepatic transport of bile alcohols in skate liver, [3H]ScyS and a potential precursor, 3α,7α,12α-trihydroxy-5β-cholestane (chtriol), were used as model compounds. Their transport into isolated hepatocytes was partially saturable, temperature sensitive, and Na+ independent. The uptake of ScyS was inhibited by cholyltaurine, and uptake of cholyltaurine was inhibited by ScyS in a competitive manner. In contrast, uptake of chtriol was not inhibited by cholyltaurine, suggesting separate transport systems. ScyS and chtriol showed a choleretic effect in isolated perfused livers. When ScyS was added to the perfusate of isolated perfused livers, >25% was found in bile within 7 h. When chtriol was added to the perfusate, 10% of the dose was secreted into the bile mainly in the form of polar metabolites, whereas only nonmetabolized chtriol remained in the livers. The slow bile flow of 40–50 μl/h and the high recovery in the liver suggest that metabolism may be the rate-limiting step in the hepatic elimination of chtriol. The major metabolites secreted into bile were identified by mass spectrometry and chromatography as scymnol and ScyS. To study the enterohepatic circulation, [3H]ScyS or [3H]chtriol was administered into the duodenum of free-swimming skates, and bile was collected through exteriorized indwelling cannulas over a 4-day period. More than 90% of the radioactivity was recovered from bile, indicating that there was a highly effective absorption in the intestinal epithelium, as well as specific transport mechanisms for hepatic uptake and biliary secretion of these compounds. This is the first direct demonstration of an enterohepatic circulation for a bile alcohol sulfate in fish liver.

scholarly journals Enzyme activity and dynamics: xylanase activity in the absence of fast anharmonic dynamics

2000 ◽  
Vol 346 (2) ◽  
pp. 355-358 ◽  
Author(s):  
Rachel V. DUNN ◽  
Valerie RÉAT ◽  
John FINNEY ◽  
Michel FERRAND ◽  
Jeremy C. SMITH ◽  
...  
Keyword(s):  
Enzyme Activity ◽  
Thermotoga Maritima ◽  
Xylanase Activity ◽  
Sharp Transition ◽  
Temperature Range ◽  
Internal Motions ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting ◽  
Single Subunit

The activity and dynamics of a simple, single subunit enzyme, the xylanase from Thermotoga maritima strain Fj SS3B.1 have been measured under similar conditions, from -70 to +10 °C. The internal motions of the enzyme, as evidenced by neutron scattering, undergo a sharp transition within this temperature range; they show no evidence for picosecond-timescale anharmonic behaviour (e.g. local diffusive motions or jumps between alternative conformations) at temperatures below -50 °C, whereas these motions are strongly activated at higher temperatures. The activity follows Arrhenius behaviour over the whole of the temperature range investigated, -70 to +10 °C. The results indicate that a temperature range exists over which the enzyme rate-limiting step is independent of fast anharmonic dynamics.

scholarly journals Nitrogen uptake and rate-limiting step in low-temperature nitriding of iron

1999 ◽  
Vol 86 (2) ◽  
pp. 810-816 ◽  
Author(s):  
D. K. Inia ◽  
A. M. Vredenberg ◽  
F. H. P. M. Habraken ◽  
D. O. Boerma
Keyword(s):  
Low Temperature ◽  
Nitrogen Uptake ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

5'-Aminolevulinate synthase activity is decreased in skeletal muscle of anemic rats

1992 ◽  
Vol 263 (2) ◽  
pp. C429-C435 ◽  
Author(s):  
L. A. McNabney ◽  
D. A. Essig
Keyword(s):  
Skeletal Muscle ◽  
Enzyme Activity ◽  
Citrate Synthase ◽  
Muscle Growth ◽  
Biosynthetic Enzyme ◽  
Deficient Diet ◽  
Aminolevulinate Synthase ◽  
Iron Deficient ◽  
Old Rats ◽  
Rate Limiting

Expression of the rate-limiting heme biosynthetic enzyme 5'-aminolevulinate synthase (ALAS) was investigated in skeletal muscle of 3-wk-old rats fed an iron-deficient diet. After 14 days, ALAS activity had declined 70% relative to control (2.1 +/- 0.2 vs. 0.6 +/- 0.1 nmol.h-1.g-1; P less than 0.005). Similar decreases were observed for blood hemoglobin (11.4 +/- 0.2 vs. 3.9 +/- 0.3 g/dl; P less than 0.005) and muscle cytochrome c (14.5 +/- 1.3 vs. 7.1 +/- 0.6 nmol/g; P less than 0.005). An iron-deficient diet decreased body and skeletal muscle growth by 15 (P less than 0.005) and 10% (P less than 0.05), respectively, whereas concentrations of protein, RNA, ALAS mRNA, and citrate synthase activity in muscle were not different from control. One mechanism by which heme biosynthesis may be slowed in muscle of young anemic rats is a decrease in ALAS activity. At a time when enzyme activity was decreased, ALAS mRNA expression was not affected by an iron-deficient diet, suggesting that steps after transcription of the ALAS gene may regulate the decrease in activity.

scholarly journals Activation and desensitization of platelets by platelet-activating factor (PAF) derived from IgE-sensitized basophils. I. Characteristics of the secretory response.

1976 ◽  
Vol 143 (4) ◽  
pp. 937-952 ◽  
Author(s):  
P M Henson
Keyword(s):  
Platelet Activating Factor ◽  
Secretory Response ◽  
Temperature Sensitive ◽  
Low Concentrations ◽  
Rabbit Platelets ◽  
Rate Limiting ◽  
Important Evidence

The secretion of vasoactive amines from rabbit platelets induced by the platelet-activating factor (PAF) derived from IgE-sensitized rabbit basophils, was examined. The secretion required calcium has previously been shown to be noncytotoxic and was optimal in both rate and extent at 37 degrees C and pH 7.2. Different temperature-sensitive steps were rate limiting for secretion above or below 20 degrees C. The rate of secretion was dependent upon the concentration of PAF and also of platelets. Maximal rates were observed with relatively low concentrations of platelets (2.5 X 10(8)/ml), sharply contrasting with other platelet stimuli such as C3 or thrombin. The extent of secretion was dependent upon PAF concentration until a maximum of 50 or 60% of the serotonin was released and then declined with increasing amounts of PAF. This was interpreted to result from the platelets becoming desensitized to the PAF, a process that shuts off the secretion. Such a desensitization was demonstrated and was shown to be stimulus specific, i.e., other stimuli could still induce secretion from PAF-desensitized platelets. PAF extracted with ethanol from the albumin to which it is usually bound during preparation, exhibited similar characteristics, except that secretion of up to 90% of the serotonin was induced. The extracted PAF thus seemed less able to induce the desensitization. Its use did provide important evidence that populations of rabbit platelets are relatively homogenous in their ability to respond to PAF.

scholarly journals New Spectrophotometric Method for the Assessment of Catalase Enzyme Activity in Biological Tissues

2019 ◽  
Author(s):  
Thulfeqar A. Hamza ◽  
Mahmoud Hussein Hadwan
Keyword(s):  
Hydrogen Peroxide ◽  
Enzyme Activity ◽  
Clinical Pathology ◽  
Biological Tissues ◽  
Ammonium Molybdate ◽  
Spectrophotometric Methods ◽  
Rate Limiting Step ◽  
Coefficients Of Variation ◽  
Rate Limiting ◽  
Health Applications

Background: Catalase is a vital antioxidant enzyme that dismutates H2O2 into water and molecular oxygen. Many protocols have been developed to measure catalase enzyme activity. Spectrophotometric methods are the most common assays that used to assess catalase enzyme activity. Methods: Because the rate-limiting step during catalase enzyme activity depends upon the dissociation of hydrogen peroxide, the developed assay measures the reaction between a hydroquinone/anilinium sulfate/ammonium molybdate reagent and Unreacted Hydrogen Peroxide, which results in the production of a purple, disubstituted quinone compound with a maximum absorbance value at 550 nm. Results: To clarify the precision of the developed method, the coefficients of variation were determined to be 2.6% and 4.7% for within run measurements and between run measurements, respectively. This method returned results that correlated well (r = 0.9982) with the results returned using the peroxovanadate method to assess catalase enzyme activity. Additionally, we examined the use of the newly developed hydroquinone assay to measure catalase enzyme activity in liver and bacterial homogenate samples. Conclusion: These results demonstrated that this assay can be used for scientific research and routine health applications because it is inexpensive, simple, accurate, and rapid. This method is suitable for use in clinical pathology laboratories because it is simple and produces precise and reproducible results.

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