| Popis: |
1. 1. Kinetic parameters of hepatic 6-phosphogluconate dehydrogenase (6PGD) from the Arctic ground squirrel were examined over the range of seasonal variation in the body temperature of the animal. 2. 2. Electrofocusing of the enzyme shows a single form of the enzyme in both hibernating and nonhibernating animals, with an isoelectric point of 5.15. 3. 3. Specific activity is significantly higher in the nonhibernator than in the hibernator, but substrate affinities for 6-phosphogluconate (6PG) and NADP + are not significantly different between the two states, or over the temperature range 5–37°C. 4. 4. ADP, ATP, Mg 2+ and fructose-1,6-bisphosphate (FBP) have no effect on enzyme activity, while AMP is mildly inhibitory ( K i = 2.18 mM). NADPH is a potent inhibitor ( K i = 0.02 mM), and may be a major regulator of 6PGD activity. 5. 5. These results suggest that the major changes in the activity of 6PGD accompanying the onset of hibernation are brought about by a combination of seasonal changes in enzyme concentration, and by the effects of a reduction in thermal energy accompanying the lowering of body temperature. |
