The Effect of Seasonal Acclimatization on Metabolic-Enzyme Activities in the Heart and Pectoral Muscle of Painted Turtles Chrysemys picta marginata

Phosphofructokinase, citrate synthase, and β-hydroxyacyl-CoA dehydrogenase activities were measured in heart and pectoral muscle from spring- and fall-acclimatized, active painted turtles. The enzyme activities derived were used as indices of glycolytic, citric acid (TCA) cycle, and β-oxidative capacities, respectively. Heart tissue exhibited significantly higher TCA cycle and β-oxidative capacities in fall relative to spring. Glycolytic capacity in the heart was similar in spring and fall and to that found in pectoral muscle. Glycolytic capacity in the pectoral muscle was slightly higher in fall, whereas β-oxidative and TCA cycle capacities remained constant across seasons. Phosphofructokinase activities in fall-acclimatized tissues were higher and less temperature sensitive in the 15-25 C than in the 5-15 C range, possibly reflecting a seasonal compensation of the temperature optima for this enzyme. The marked changes in cardiac TCA cycle and β-oxidative capacities and the relative stability of glycolytic capacities between spring and fall show a seasonal shift in the enzyme profile of this tissue type. The TCA cycle and β-oxidative pathways potentially provide more energy during activity in fall, a conclusion corroborated by system-correlation ratios. Glycolytic capacity is maintained in both tissue types across seasons, suggesting that glycolysis is important for supplying energy over a wide range of conditions.