Abstract
Kinetic properties of regulatory enzymes of glycolysis in liver of the mouse, Zapus hudsonius, were modified during hibernation, the probable mechanism being covalent modification. Liver glycogen phosphorylase activity was strongly depressed during both short (less than 24 h) and long (5-8 days) term hibernation, the mechanism involving a decrease in both the percentage of enzyme in the active a form and the total amount (a + b) of enzyme expressed. Phosphofructokinase showed kinetic changes (a 2.5-fold increase in Ka for fructose-2,6-P2, 4- and 3.7-fold decreases in I50 values for ATP and citrate, compared to euthermic controls) in liver of hibernators indicative of phosphorylation inactivation of the enzyme. Measured levels of fructose-2,6-P2 in liver did not change during hibernation. Changes in pyruvate kinase kinetics in liver from long term hibernators similarly indicated enzyme phosphorylation in the depressed state (Ka for fructose-1,6-P2 increased 4.4-fold, I50 for L-alanine decreased 6.3-fold). Apparent covalent modification of glycolytic enzymes during hibernation may serve two functions: depression of glycolytic activity as part of the general metabolic rate depression of hibernation, or reorganization of fuel use in the hibernating state to limit carbohydrate catabolism and promote gluconeogenesis.
Highlights
The biochemical basis of metabolic rate depression during being covalent modification
Phosphofructokinase showed kinetic changes (a 2.5-fold increase in terms, Qlo values ranging from 2.0 to 4.5 have been reported for the euthermia to hibernation transition[8].Lower values for Qlo suggest that the metabolic rate reduction observed is that expected wheneuthermic uersus hibernating body temperatures are considered; higher values imply additional
The fall in body temperature during entry of fructose-2,6-P2in liver did not change during hiber- into hibernation is the result of a coordinated reduction in nation
Summary
Becauseindividualbehaviorinfluenced entry into hibernation,thelength of hibernation(with body temperature equilibratedtoambient)variedsomewhat for individuals within each experimental group. Animals in the short-term experimental group had been in hibernation for less than 24 h (but longer than 8 h). Animals allowed long-term hibernation had been in continuous torpor fo5r-8 days
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