Comparative Study of Lactate Dehydrogenase Activity in Diving and Nondiving Reptiles

The properties of lactate dehydrogenase (LDH) were examined in two snake species and one turtle species. The snakes used in the study were the semi-aquatic Nerodia rhombifera and the terrestrial Elaphe obsoleta, while Pseudemys scripta represented the turtle species. Our purpose was to compare the LDH activity of nondiving reptiles (Nerodia and Elaphe) with that of the well established diver Pseudemys. The kinetic properties of LDH and its susceptibility to inhibition by elevated pyruvate concentrations were investigated in the brain and heart of the three species. Brain and heart were chosen because they are highly aerobic tissues and therefore should be quite sensitive to anoxia. In both tissues the LDH activity of the snakes was higher than that of Pseudemys at pyruvate concentrations ranging between .03 mM and .50 mM. The Km values of the snakes were lower than those of Pseudemys in both tissues suggesting a greater enzyme-substrate affinity in the snake tissues. The Vmax values were higher in snake brain and heart than in turtle indicating a faster conversion of substrate to product in the snake tissues. Brain LDH activity was reduced by high pyruvate concentrations to an equal extent in the three species. Nerodia heart LDH showed the greatest susceptibility to substrate inhibition while heart LDH activity was equally inhibited in Elaphe and Pseudemys. The results indicate that the LDH of Pseudemys is no better adapted to anaerobic conditions than that of Nerodia and Elaphe