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 character-istic of body temperatures in euthermia vs. hibernation. The enzyme showed reduced sensitivity to all activators at 5 C, theKa 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. .
