Mitochondrial α-glycerophosphate dehydrogenase activity in active and torpid ground squirrels, Spermophilus richardsoni

Abstract

1. 1. Mitochondrial α-glycerophosphate dehydrogenase (GPD) activity was assayed in liver homogenates from active and torpid ground squirrels. 2. 2. Arrhenius plots of GPD activity were linear in non-hibernating animals and discontinuous in hibernators. Compared with non-hibernators, the energy of activation in hibernators was reduced between 37 and 25°C, but increased between 25 and 6°C. 3. 3. A dose-response relation between GPD activity and injected thyroxine was determined in active animals. No correlation was found between enzyme activity at 37 or 6°C and circulating titres of thyroid hormones, in ground squirrels sampled during the preparative and hibernating phases.