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  • 1
    Electronic Resource
    Electronic Resource
    Differential sensitivities to hypoxia by two anoxia-tolerant marine molluscs: A biochemical analysis (1991)
    Springer
    Marine biology 111 (1991), S. 343-351 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The metabolic responses to a series of low oxygen tensions were compared for two species of Mediterranaean bivalves,Mytilus galloprovincialis andScapharca inaequivalvis. Whereas both species have well-developed and similar tolerances of anoxia, the metabolic responses ofS. inaequivalvis to low oxygen tensions indicate a substantially greater tolerance of hypoxia. Compared withM. galloprovincialis, the responses ofS. inaequivalvis included the ability to maintain a constant oxygen consumption down to a much lower pO2 value (ca. 1.7 vs 3.4 ppm), and a lower critical pO2 for the recruitment of fermentative pathways of ATP production (ca. 1 vs 3 ppm). Furthermore, a graded increase in the output of anaerobic products (succinate, alanine) occured at oxygen tensions below 3 ppm inM. galloprovincialis and reached a maximum at 1.6 ppm whereas inS. inaequivalvis the net accumulation of anaerobic products at the lowest oxygen tension tested (0.5 ppm) was still substantially less than the level of production output in complete anoxia. This suggests that fermentative pathways are maximally activated at all oxygen tensions below 1.6 ppm inM. galloprovincialis whereas rates of anaerobic pathways are still less than maximum at 0.5 ppm inS. inaequivalvis. These results indicate that in situations of declining oxygen tensions, such as occur due to eutrophication,M. galloprovincialis would not only begin to experience metabolic stress at higher oxygen tensions thanS. inaequivalvis but would experience greater stress at any given pO2. Such differences in hypoxia tolerances may explain the success of the recently introducedS. inaequivalvis in out-competing the nativeM. galloprovincialis in the Adriatic Sea.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01319405
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  • 2
    Electronic Resource
    Electronic Resource
    Cyclic AMP-dependent protein kinase: role in anoxia and freezing tolerance of the marine periwinkle Littorina littorea (1999)
    Springer
    Marine biology 133 (1999), S. 193-203 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A key regulatory mechanism underlying the switch between aerobic and anaerobic metabolism amongst anoxia-tolerant marine molluscs is reversible protein phosphorylation. To assess the role of cAMP-dependent protein kinase (PKA) in aerobic–anaerobic transitions, the effects of anoxia on the activity and subcellular distribution of PKA were assessed in foot and hepatopancreas of the marine periwinkle, Littorina littorea. Exposure to N2 gas at 5 °C caused a rapid decline in the percentage of total enzyme present as the free catalytic subunit (PKAc) in both tissues; the percentage of PKAc fell from ∼30% in controls to 3% after 1 h anoxia and remained low over 72 h. Total PKA also fell by 30% after 72 h anoxia in hepatopancreas but rebounded during aerobic recovery. Freezing at −8 °C elicited parallel results for both percentage of PKAc and total PKA, suggesting that PKA responses to freezing were stimulated by the ischemia that develops when hemolymph freezes. Anoxia also led to a shift in PKA subcellular distribution in hepatopancreas (but not in foot), the percentage of total PKA activity associated with the nuclear fraction dropping from 25% in controls to 8% in 12 h anoxic snails with opposite changes in the cytosolic fraction. The catalytic subunit (PKAc) of foot PKA was purified to a final specific activity of 63.5 nmol phosphate transferred per minute per milligram protein. Enzyme properties included a molecular weight of 33 to 35 kDa, an activation energy from Arrhenius plots of 65.1 ± 4.8 kJ mol−1, and substrate affinity constants of 151 ± 6 μM for the phosphate acceptor, Kemptide, and 72 ± 9 μM for Mg.ATP. Activity was strongly reduced by mammalian PKA inhibitors (H-89, PKA-I), by neutral chloride salts (I50 values 165 to 210 mM) and by NaF (I50 62 mM). Reduced PKA activity under anoxic or freezing conditions would facilitate the observed suppression of the activities of numerous enzymes that are typically PKA-activated and thereby contribute to the overall anoxia-induced metabolic rate depression.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270050458
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  • 3
    Electronic Resource
    Electronic Resource
    Regulation of glycolytic enzymes in the marine invertebrateHalicryptus spinulosus (Priapulida) during environmental anoxia and exposure to hydrogen sulfide (1990)
    Springer
    Marine biology 106 (1990), S. 261-266 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A particularly strong reduction of metabolic activity is a precondition for long-term survival ofHalicryptus spinulosus von Siebold under anoxic habitat conditions because of its relatively low fuel reserves (mainly glycogen). The present study analyses the mechanism of this metabolic slow-down. For this purpose the effects of environmental anoxia and exposure to hydrogen sulfide on the activity and selected kinetic properties of glycolytic enzymes [glycogen phosphorylase (GP), pyruvate kinase (PK)] and the concentrations of fructose-2,6-bisphosphate in the body wall ofH. spinulosus were analysed. Anoxia and hydrogen sulfide exposure stimulated modifications of the properties of the enzymes, in both cases due to probable covalent modification of the enzyme proteins. Under both conditions phosphorylase activity was depressed by about 1/3, the result of changes in the percentage of enzyme in the activea-form as well as the total amount of enzyme activity expressed (a +b). Effects of anoxia on the properties of pyruvate kinase included reducedV max , decreasedS 0.5 for phospho-enolpyruvate, changes inK a for fructose-1,6-bisphosphate (an initial decrease was followed by a later increase). TheI 50 forL-alanine of PK was extremely reduced under anoxia and showed an even greater sensitivity to the presence of hydrogen sulfide. Anoxia stimulated a slight reduction in the content of fructose-2,6-bisphosphate, whereas exposure to hydrogen sulfide caused a dramatic decrease of this allosteric activator of phos-phofructokinase. The study gives evidence that mechanisms of glycolytic rate depression are conserved within a wide variety of vertebrate and invertebrate phyla. With two exceptions (fructose-2,6-bisphosphate levels and alanine inhibition of PK) the responses to hydrogen sulfide were the same as those to anoxia, suggesting that at a metabolic level, the consequences of each stress on energy metabolism are similar.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01314809
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  • 4
    Electronic Resource
    Electronic Resource
    Natural Freeze Tolerance in Ectothermic Vertebrates (1992)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physiology 54 (1992), S. 619-637 
    Details
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.ph.54.030192.003155
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  • 5
    Electronic Resource
    Electronic Resource
    Freeze tolerance in the frog,Rana sylvatica (1984)
    Springer
    Cellular and molecular life sciences 40 (1984), S. 1261-1262 
    Details
    ISSN: 1420-9071
    Keywords: Rana sylvatica ; frog, freeze tolerance ; cryoprotectant synthesis ; glycogen levels, liver ; glucose levels, cryoprotectant
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Wood frogs survive extracellular freezing at moderate subzero temperatures (−4°C) for at least 11 days. Freezing survival is aided by the accumulation of high concentrations of glucose as a cryoprotectant in blood and tissues. Glucose production was accompanied by a rapid decline in liver, but not muscle, glycogen levels suggesting that liver is the organ controlling cryoprotectant synthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01946664
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  • 6
    Electronic Resource
    Electronic Resource
    Gluconeogenesis in trout (Oncorhynchus mykiss) white muscle: purification and characterization of fructose-1,6-bisphosphatase activity in vitro (1992)
    Springer
    Fish physiology and biochemistry 10 (1992), S. 201-212 
    Details
    ISSN: 1573-5168
    Keywords: rainbow trout ; Oncorhynchus mykiss ; white muscle ; enzyme ; purification ; gluconeogenesis ; pH ; fructose-1,6-bisphosphatase ; phosphofructokinase ; exercise
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Studies of the enzyme fructose-1,6-bisphosphatase (FBPase) of rainbow trout (Oncorhynchus mykiss) have been undertaken in order to illuminate aspects of skeletal muscle gluconeogenesis in these animals. Maximal activities in crude homogenates of several organs suggest that the liver possesses the greatest FBPase activity on a unit g−1 tissue basis but that the white muscle, owing to its bulk, contributes substantially to whole body FBPase activity. Studies of fructose-6-phosphate-1-kinase (PFK) and FBPase in crude homogenates of several organs suggests an important role for intracellular pH in regulating the relative carbon flux through the FBPase/PFK locus in vivo. Furthermore, a three-step purification scheme is described for trout white muscle FBPase by which a stable and homogeneous (by SDS PAGE) enzyme preparation (isoelectric point = 7.2; molecular weight = 37.6 kd) was obtained. Kinetic studies of the purified enzyme were undertaken at 20°C under conditions reflective of "rest" and "exercise/recovery" intramuscular pH in vivo. Affinity for substrate (F-1,6-P2) was increased (Km = 6.88 versus 2.44 μmol 1-−1 as was enzyme activity when pH was lowered from 7.0 to 6.5. Various inhibitor metabolites are identified including F-2,6-P2 (mixed-type inhibitor, Ki = 0.201 μmol 1−1, pH 7.0) and AMP (non-competitive inhibitor, Ki = 0.438 μmol 1−1, pH 7.0). Inhibition by F-2,6-P2 was strongly alleviated by a reduction in pH from 7.0 to 6.5 (I50 increased from 0.14 to 0.32 μmol 1−1). AMP on the other hand was a more potent inhibitor at pH 6.5 but this inhibition was totally reversed under conditions of citrate, NH4 + and AMP typical of muscle during recovery from exercise in vivo. In purified white muscle enzyme preparations, FBPase demonstrated maximal activity at pH 6.5 whereas the optimal pH of PFK was 7.0 or greater. Indeed, it appears from these in vitro data that regulation by metabolite levels as well as pH are required for net FBPase flux in vivo. It is concluded, therefore that trout white muscle FBPase demonstrates the potential to play an important enzymatic role in the control of intramuscular gluconeogenesis in these animals. The results are discussed in relation to present knowledge regarding the metabolic responses of trout white muscle to, and its subsequent recovery from, exhaustive exercise.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00004514
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  • 7
    Electronic Resource
    Electronic Resource
    Influence of exercise on the distribution of enzymes in trout white muscle and kinetic properties of AMP-deaminase from free and bound fractions (1994)
    Springer
    Fish physiology and biochemistry 13 (1994), S. 407-418 
    Details
    ISSN: 1573-5168
    Keywords: Oncorhynchus mykiss ; phosphofructokinase ; fructose- 1,6-bisphosphatase ; enzyme binding ; exercise ; AMP-deaminase regulatory properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Effects of exercise on the distribution of phosphofructokinase (PFK), fructose-1,6-biphosphatase (FBPase), and AMP-deaminase between free and particulate-bound fractions was analyzed in white skeletal muscle of rainbow trout Oncorhynchus mykiss. With a widely used technique for the separation of free and bound enzyme fractions (homogenization in low ionic strength, high sucrose buffer), the data showed that the amount of bound PFK increased from 64 to 95% during burst swimming whereas other enzymes were unaffected. Since this data for AMP-deaminase contrasted with earlier reports, different methods of separating free and bound enzyme were evaluated. A clear effect of exercise on AMP-deaminase binding occurred when high ionic strength media (either KCl or KF) were used; in extraction media containing 150 mM KCl, the percent bound rose from 30% in controls to 97% after 1 min burst swimming. Exercise also produced stable changes to AMP-deaminase kinetic properties, including for the bound enzyme (compared with the free) a 2-fold higher Km AMP, a 3-fold higher Ki for inorganic phosphate, and a 60% increase in Ka ADP after 1 min burst exercise. The data suggest that AMP-deaminase in working skeletal muscle is subject to combined controls by allosteric effectors, post-translational modification, and distribution between free and bound states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00003420
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  • 8
    Electronic Resource
    Electronic Resource
    Deoxyribose degradation catalyzed by Fe(III)-EDTA: kinetic aspects and potential usefulness for submicromolar iron measurements (1994)
    Springer
    Molecular and cellular biochemistry 137 (1994), S. 65-73 
    Details
    ISSN: 1573-4919
    Keywords: iron ; iron quantification ; deoxyribose degradation ; 2-deoxy-D-ribose ; thiobarbituric acid reactive substances ; hydroxyl radical ; superoxide radical ; copper
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Iron ions play a central role in ·OH radicals formation and induction of oxidative stress in living organisms. Ironcatalyzed ·OH radical formation degrades deoxyribose to thiobarbituric acid reactive substances (TBA-RS). This paper analyzes kinetic properties of the Fe(III)-EDTA-catalyzed deoxyribose degradation in the presence of ascorbate. The yield of TBA-RS formation in the presence of EDTA was 4-fold higher than in its absence, contrasting with results reported elsewhere, Cu(II)-EDTA and Fe(III)-citrate were unable to catalyze deoxyribose degradation. The dependence on deoxyribose concentration was fitted to a Lineweaver Burk-like plot and it was calculated that approximately 4.5 mM deoxyribose scavenged half of the ·OH radicals formed. The data for Fe(III)-EDTA concentration dependence could also be fitted to a rectangular hyperbolic function. This function was linear up to 1 μM added FeCl3 and this property could be utilized as an assay for the estimation of submicromolar iron concentrations. Submicromolar concentrations of iron could induce measurable yields of TBA-RS. Differences of as little as 0.1 μM Fe(III)-EDTA could be reproducibly detected under optimum experimental conditions, above a consistent background absorbance that was equivalent to 0.35±0.05 μM Fe(III)-EDTA and represented contaminating iron in the reactants that could not be removed with Chelex-100. The low method determination limit makes the deoxyribose degradation reaction potentially useful as a new, highly sensitive and cost effective assay for iron quantification.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00926041
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  • 9
    Electronic Resource
    Electronic Resource
    Evidence for aestivation specific proteins inOtala lactea (1995)
    Springer
    Molecular and cellular biochemistry 143 (1995), S. 15-20 
    Details
    ISSN: 1573-4919
    Keywords: aestivation ; protein synthesis ; stress protein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Changes in [35S]methionine protein labeling patterns were examined by following incorporation into the acid precipitate protein fraction of land snails,Otala lactea (Müller) (Pulmonata, Helicidae). Labeled proteins were analyzed by SDS polyacrylamide gel electrophoresis and isoelectric focusing columns. Snails in four different physiological states were compared: active controls, short term aestivating snails (injected and allowed to enter aestivation), long term aestivating snails (aestivated for 14 days, injected, and maintained in the aestivating state), and snails aroused after aestivation (aestivated, injected, and aroused). Protein associated radioactivity was measured over a 7 day time course post injection. Autoradiographic analysis of SDS-polyacrylamide gels showed increases in the radioactivity of four proteins: 91 kDa (hepatopancreas, day 1 in long term aestivating animals), 50 kDa (hepatopancreas, day 2 in short term aestivating snails), 70 kDa and 30 kDa (foot, day 2 in short term aestivating animals). Hepatopancreas and foot from day 1 long term aestivating and day 2 short term aestivating animals were also analyzed by isoelectric focusing columns. Several pH-specific differences were apparent when controls and aestivating animals were analyzed. In particular a peak of radioactivity was observed at pH 5.05 in 1 d long term aestivating hepatopancreas and at pH 4.30 in 2d short term aestivating animals. Several differences were noted in foot with no specific pattern emerging. SDS-polyacrylamide gel electrophoresis analysis of the hepatopancreas peaks showed the appearance of several bands with increased radioactivity, including the 91 kDa and 50 kDa proteins described above. These results suggest thatO. lactea aestivation specific proteins may be involved in the transition to a depressed metabolic state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00925922
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  • 10
    Electronic Resource
    Electronic Resource
    Role of glucose and insulin in regulating glycogen synthase and phosphorylase activities in rainbow trout hepatocytes (1995)
    Springer
    Journal of comparative physiology 165 (1995), S. 62-70 
    Details
    ISSN: 1432-136X
    Keywords: Glycogen ; Hepatocyte ; Insulin ; 13C NMR ; Rainbow trout, Oncorhynchus mykiss
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract This study, using 13C nuclear magnetic resonance spectroscopy showed enrichment of glycogen carbon (C1) from 13C-labelled (C1) glucose indicating a direct pathway for glycogen synthesis from glucose in rainbow trout (Oncorhynchus mykiss) hepatocytes. There was a direct relationship between hepatocyte glycogen content and total glycogen synthase, total glycogen phosphorylase and glycogen phosphorylase a activities, whereas the relationship was inverse between glycogen content and % glycogen synthase a and glycogen synthase a/glycogen phosphorylase a ratio. Incubation of hepatocytes with glucose (3 or 10 mmol·1-1) did not modify either glycogen synthase or glycogen phosphorylase activities. Insulin (porcine, 10-8 mol·1-1) in the medium significantly decreased total glycogen phosphorylase and glycogen phosphorylase a activities, but had no significant effect on glycogen synthase activities when compared to the controls (absence of insulin). In the presence of 10 mmol·1-1 glucose, insulin increased % glycogen synthase a and decreased % glycogen phosphorylase a activities in trout hepatocytes. Also, the effect of insulin on the activities of % glycogen synthase a and glycogen synthase a/glycogen phosphorylase a ratio were more pronounced at low than at high hepatocyte glycogen content. The results indicate that in trout hepatocytes both the glycogen synthetic and breakdown pathways are active concurrently in vitro and any subtle alterations in the phosphorylase to synthase ratio may determine the hepatic glycogen content. Insulin plays an important role in the regulation of glycogen metabolism in rainbow trout hepatocytes. The effect of insulin on hepatocyte glycogen content may be under the control of several factors, including plasma glucose concentration and hepatocyte glycogen content.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00264687
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