Purification and characterization of skeletal muscle pyruvate kinase from the hibernating ground squirrel, Urocitellus richardsonii: potential regulation by posttranslational modification during torpor.

Ground squirrel torpor during winter hibernation is characterized by numerous physiological and biochemical changes, including alterations to fuel metabolism. During torpor, many tissues switch from carbohydrate to lipid catabolism, often by regulating key enzymes within glycolytic and lipolytic pathways. This study investigates the potential regulation of pyruvate kinase (PK), a key member of the glycolytic pathway, within the skeletal muscle of hibernating ground squirrels. PK was purified from the skeletal muscle of control and torpid Richardson's ground squirrels, and PK kinetics, structural stability, and posttranslational modifications were subsequently assessed. Torpid PK displayed a nearly threefold increase in K _m PEP as compared to control PK when assayed at 5 °C. ProQ Diamond phosphoprotein staining as well as phospho-specific western blots indicated that torpid PK was significantly more phosphorylated than the euthermic control. PK from the torpid condition was also shown to possess nearly twofold acetyl content as compared to control PK. In conclusion, skeletal muscle PK from the Richardson's ground squirrel may be regulated posttranslationally between the euthermic and torpid states, and this may inhibit PK functioning during torpor in accordance with the decrease in glycolytic rate during dormancy.