Temperature and phosphate effects on allosteric phenomena of phosphofructokinase from a hibernating ground squirrel (Spermophilus lateralis)
Temperature effects on the kinetic properties of phosphofructokinase (PFK) purified from skeletal muscle of the golden-mantled ground squirrel, Spermophilus lateralis, were examined at 37 °C and 5 °C, values characteristic of body temperatures in euthermia vs. hibernation. The enzyme showed reduced sensitivity to all activators at 5 °C, the Ka values for AMP, ADP, NH4 + and F2,6P2 were 3-11-fold higher at 5 °C than at 37 °C. Inhibition by citrate was not affected whereas phosphoenolpyruvate, ATP and urea became more potent inhibitors at low temperature. While typically considered an activator of PFK activity, inorganic phosphate performed as an inhibitor at 5 °C. Decreasing temperature alone causes the actions of inorganic phosphate to change from activation to inhibition. We found that Km values for ATP remained constant while Vmax dropped significantly upon the addition of phosphate. Phosphate inhibition at 5 °C was noncompetitive with respect to ATP and the Ki was 0.15 ± 0.01 mM (n = 4). The results indicate that PFK is less likely to be activated in cold torpid muscle; PFK is less sensitive to changing adenylate levels at the low temperatures characteristic of torpor, and PFK is clearly much less sensitive to biosynthetic signals. All of these characteristics of hibernator PFK would serve to reduce glycolytic rate and help to preserve carbohydrate reserves during torpor.
|Keywords||Glycolysis, Mammalian hibernation, Metabolic rate depression, Phosphofructokinase, Temperature effects|
MacDonald, J.A. (Justin A.), & Storey, K. (2005). Temperature and phosphate effects on allosteric phenomena of phosphofructokinase from a hibernating ground squirrel (Spermophilus lateralis). FEBS Journal, 272(1), 120–128. doi:10.1111/j.1432-1033.2004.04388.x