Purification and characterization of fructose bisphosphate aldolase from the ground squirrel, Spermophilus lateralis: enzyme role in mammalian hibernation

Fructose-1,6-bisphosphate (F1,6P2) aldolase was purified to homogeneity from skeletal muscle of the golden-mantled ground squirrel, Spermophilus lateralis. Enzyme properties were examined at temperatures characteristic of euthermia (37 °C) and hibernation (5 °C); parallel studies assessed rabbit muscle aldolase for comparison. Kinetic properties of each enzyme were differentially affected by assay temperature. For example, the Km for F1,6P2 of ground squirrel aldolase was 0.9±0.05 μM at 37 °C and 50% higher (1.45±0.04 μM) at 5 °C, whereas the Km of rabbit aldolase increased threefold over the same temperature range. The inhibitory effects of adenylates were similar at both temperatures for the ground squirrel enzyme, but inhibition by adenosine 5′-diphosphate, adenosine 5′-monophosphate, and inosine 5′-monophosphate was substantially reduced at 5 °C for rabbit aldolase. Inhibition by inorganic phosphate increased at lower temperatures for both enzymes; for ground squirrel aldolase, the Ki was 1.18±0.1 mM at 37 °C and 0.23±0.05 mM at 5 °C. Inhibition of aldolase by inorganic phosphate could be one factor that helps to shut down glycolysis during hibernation. Thus, mammalian hibernators may exploit low-temperature characteristics of aldolase to benefit the metabolic needs of the hibernating state.