Regulation of enzyme activity in the hibernator: Effect of cations on liver pyruvate kinase in the arctic ground squirrel

1981 ◽  
Vol 6 (1) ◽  
pp. 31-34 ◽  
Author(s):  
Hans W. Behrisch ◽  
W.A. Galster
Keyword(s):  
Enzyme Activity ◽  
Pyruvate Kinase ◽  
Ground Squirrel ◽  
The Arctic ◽  
Arctic Ground Squirrel ◽  
Regulation Of Enzyme Activity

Regulation of enzyme activity in the hibernator. A kinetic and spectroscopic study of muscle pyruvate kinase from the Arctic ground squirrel

1981 ◽  
Vol 59 (9) ◽  
pp. 762-769 ◽  
Author(s):  
George A. Morse ◽  
Hans W. Behrisch
Keyword(s):  
Pyruvate Kinase ◽  
Ground Squirrel ◽  
Arrhenius Plot ◽  
Gel Filtration ◽  
The Arctic ◽  
Subunit Interaction ◽  
Arctic Ground Squirrel ◽  
Derivative Spectroscopy ◽  
Muscle Pyruvate Kinase ◽  
Regulation Of Enzyme Activity

Pyruvate kinase skeletal muscle of the Arctic ground squirrel was purified to homogeneity. The purified enzyme variants from the summer-active and winter hibernating squirrel appear to be identical with a near-neutral pI of 6.9 and a molecular weight of 234 000 as determined by gel filtration chromatography on Bio-Gel A-0.5m. Evidence for subunit interaction during inhibition by L-phenylalanine is demonstrated with ultraviolet derivative spectroscopy. A model for this interaction and its importance for a regulatory role are discussed. The absence of a temperature break in the Arrhenius plot for the pyruvate kinase reaction, the kinetic and physical data, and the near-neutral pI, suggest an amino acid composition that conserves the overall geometry and resultant kinetic behavior which render regulation of the enzyme insensitive to temperature.

Temperature and the Regulation of Enzyme Activity in the Hibernator. Isoenzymes of Liver Pyruvate Kinase from the Hibernating and Non-hibernating Arctic Ground Squirrel

1974 ◽  
Vol 52 (10) ◽  
pp. 894-902 ◽  
Author(s):  
Hans W. Behrisch
Keyword(s):  
Molecular Weight ◽  
Pyruvate Kinase ◽  
Wide Temperature Range ◽  
Ground Squirrel ◽  
Energy Charge ◽  
High Energy ◽  
Ground Squirrels ◽  
The Arctic ◽  
Arctic Ground Squirrel ◽  
Temperature Range

Liver of the hibernating (H) Arctic ground squirrel (Citellus undulatus) contains a single species of pyruvate kinase (PyK) that is distinct from the single isoenzyme of pyK observed in the non-hibernating (NH) ground squirrel, which has been previously described (Behrisch &Johnson (1974) Can. J. Biochem. 52, 547–559). The H-PyK has a pI value of 5.7 and a molecular weight of 241 000 – 243 000. Affinity of the H-PyK for the substrates phosphoenolpyruvate (PEP) and ADP is not affected by changing temperature. It is argued that this stability of the apparent Km's for substrate over a wide temperature range permits the hibernator to take advantage of the Q10 effect in maintaining a low rate of the PyK reaction. Similarly, affinity of H-PyK for the allosteric activator fructose-1,6-phosphate (FDP) and the inhibitor ATP is also conspicuously independent of temperature, suggesting a fine stoichiometry in the relative concentrations of the regulatory ligands in control of H-PyK over a wide temperature range. Further, affinity of H-PyK for the inhibitor ATP is about three- to fourfold lower than that of the NH-PyK, a condition that would favor the maintenance of a high energy charge in the hibernating liver cell. ATP apparently inhibits PyK by causing a dissociation of the enzyme molecule into two "halves" of about 110 000 molecular weight each. This dissociation is offset and reversed by FDP. Removal of the ATP by dialysis does not of itself result in a reassociation of the PyK "halves"; FDP and/or the substrates are required for the two subunits of PyK to reassociate. As the apparent Ki of H-PyK for ATP is higher than that of NH-PyK, substantially higher concentrations of ATP are required to effect the dissociation of H-PyK. Similarly, elevated concentrations of FDP are required to offset the ATP-caused dissociation of the H-PyK.Hibernating Arctic ground squirrels that are preparing to emerge finally from the hibernating state already possess substantial activities of the NH-PyK isoenzyme. This suggests that the animal "anticipates" its transition from one metabolic state from another. On the basis of these data a formal mechanism is proposed for the regulation of liver PyK in the Arctic ground squirrel in both the non-hibernating and hibernating states.

Regulatory Properties of Pyruvate Kinase from Liver of the Summer-Active Arctic Ground Squirrel

1974 ◽  
Vol 52 (6) ◽  
pp. 547-559 ◽  
Author(s):  
Hans W. Behrisch ◽  
Craig E. Johnson
Keyword(s):  
Pyruvate Kinase ◽  
Ground Squirrel ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Effect Of Temperature ◽  
Arctic Ground Squirrel ◽  
Physiological Importance ◽  
Atp Inhibition ◽  
High Concentrations ◽  
Regulatory Properties ◽  
Regulation Of Enzyme Activity

The properties of liver pyruvate kinase (PyK) from summer-active Arctic ground squirrel (Citellus undulatus) were examined over the physiological temperature range of the animal. One form of the enzyme with a pI (isoelectric point) value of 5.3 was observed and exhibited kinetics similar to those of L-type PyK. This form has a molecular weight of 243 000, similar to that of M-type PyK. Enzyme–phosphoenolpyruvate (PEP) affinity falls with decreasing temperature while affinity for ADP increases under these conditions. The effect of temperature upon extent of negative cooperativity of PEP binding and its possible physiological importance are briefly discussed. Fructose-1,6-phosphate (FDP) increases the affinity of PyK for PEP but has no effect upon enzyme-ADP interaction. However, Vmax in the presence of saturating concentrations of both substrates is increased two to threefold by FDP, the allosteric activator. Ground squirrel PyK is inhibited by ATP. Inhibition by ATP of PyK activity is diminished by decreasing the temperature or by increasing the concentrations of substrate. FDP reverses this inhibition but the degree of reversal is sensitive to substrate concentration and temperature. Inhibition by ATP is competitive for the PEP site and appears to be of the "mixed-competitive" variety when carried out at varying concentrations of ADP. Inhibition by alanine is noncompetitive for both substrate sites. As a result of the very high concentrations of amino acids needed to obtain appreciable inhibition of live PyK, this does not appear to be a physiological means of regulation of enzyme activity. The effect of intermediates of the glycolytic, pentose shunt, and Krebs acid cycle pathways upon PyK activity is briefly discussed. Inosine nucleotides, involved in the reversal of the PyK reaction by phosphoenolpyruvate carboxykinase, have a strong modulating effect upon PyK activity. These data suggest formal mechanisms for the regulation of liver PyK in the ground squirrel.

scholarly journals Resistance to Systemic Inflammation and Multi Organ Damage after Global Ischemia/Reperfusion in the Arctic Ground Squirrel

PLoS ONE ◽  
2014 ◽  
Vol 9 (4) ◽  
pp. e94225 ◽  
Author(s):  
Lori K. Bogren ◽  
Jasmine M. Olson ◽  
JoAnna Carpluk ◽  
Jeanette M. Moore ◽  
Kelly L. Drew
Keyword(s):  
Systemic Inflammation ◽  
Ground Squirrel ◽  
Ischemia Reperfusion ◽  
Organ Damage ◽  
Global Ischemia ◽  
The Arctic ◽  
Arctic Ground Squirrel

Fat Metabolism in the Arctic Ground Squirrel

1950 ◽  
Vol 31 (3) ◽  
pp. 304 ◽  
Author(s):  
Charles G. Wilber ◽  
X. J. Musacchia
Keyword(s):  
Ground Squirrel ◽  
Fat Metabolism ◽  
The Arctic ◽  
Arctic Ground Squirrel

scholarly journals Arctic ground squirrel population collapse in the boreal forests of the Southern Yukon

2015 ◽  
Vol 42 (2) ◽  
pp. 176 ◽  
Author(s):  
Jeffery R. Werner ◽  
Charles J. Krebs ◽  
Scott A. Donker ◽  
Rudy Boonstra ◽  
Michael J. Sheriff
Keyword(s):  
Boreal Forest ◽  
Ground Squirrel ◽  
Boreal Forests ◽  
Ground Squirrels ◽  
The Arctic ◽  
Arctic Ground Squirrel ◽  
Forest Zone ◽  
Winter Climate ◽  
Population Collapse ◽  
Predator Pit

Context The arctic ground squirrel (Urocitellus parryii) comprised 17% of the biomass of herbivores in the Yukon boreal forest during the summer months from 1987 to 1996 and was responsible for 23% of the energy flow at the herbivore level. By 2000, ground squirrel populations in this region collapsed to nearly zero and have remained there. Aims We summarise the population monitoring (since 1975) and recent experimental work that has been done on this key herbivore in the Kluane area of the southern Yukon to test one mechanistic hypothesis as the possible explanation for this population collapse and subsequent lack of recovery: predation. Methods Ground squirrels are the preferred summer prey of bird and mammal predators when snowshoe hare (Lepus americanus) populations are declining. We used translocations into formerly occupied habitat and radiotelemetry to determine movements and causes of death from 2009 to 2014. We surveyed 158 sites between 2008 and 2013 to measure the disappearance of colonies in alpine and forest habitats over 25 000 km2. Key results Ground squirrels from 2000 to 2013 comprised a small fraction of the herbivore biomass in the boreal forest zone, down from 17% earlier. Most forest populations (~95%) are currently extinct, whereas just over half (65%) of low-elevation meadow populations are locally extinct. One hypothesis is that ground squirrels in the forest have been driven into a predator pit from which they cannot recover. They remain abundant in alpine tundra (93% occupancy rate) and around airport runways and human habitations (97% occupancy), but there is no apparent dispersal from alpine areas down into the boreal forest. Conclusion The predator pit hypothesis is a likely explanation for the initial collapse and sustained decline in population size from 2000 to 2013. Recent attenuation of the hare cycle and milder winter climate have allowed shrubs to expand throughout the forest, thereby reducing visibility and increasing predation risk. This conclusion will be tested in further research using reintroductions to formerly occupied sites. Implication If the loss of this herbivore from the boreal forest is not reversed, predator pressure on the other major herbivores of the montane forest zone is likely to change significantly.

scholarly journals EVOLUTIONARY HISTORY OF THE ARCTIC GROUND SQUIRREL (SPERMOPHILUS PARRYII) IN NEARCTIC BERINGIA

2004 ◽  
Vol 85 (4) ◽  
pp. 601-610 ◽  
Author(s):  
Aren A. Eddingsaas ◽  
Brandy K. Jacobsen ◽  
Enrique P. Lessa ◽  
Joseph A. Cook
Keyword(s):  
Ground Squirrel ◽  
Evolutionary History ◽  
The Arctic ◽  
Arctic Ground Squirrel ◽  
Spermophilus Parryii ◽  
History Of
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