Adaptative features of ectothermic enzymes--II. The effects of acclimation temperature on the malate dehydrogenase of the spot. Leiostomus xanthurus.

1. Isozyme patterns and thermostability of the skeletal muscle and heart malate dehydrogenase (s-MDH) from the spot acclimated to different temperatures were examined. 2. No changes in isozyme patterns were seen for MDH in any of the tissues examined in response to 15 degrees and 20 degrees C acclimation. 3. The A-homodimer, which was more thermostable showed an increase in its relative activity, whereas the B-homodimer, which was more heat sensitive, showed a decrease during warm acclimation. However, after different periods of low temperature incubation, these samples showed a decrease in their subunit ratios. 4. Concerning the effect to thermal acclimation on the thermostability of MDH, it was found that skeletal muscle samples of the 30 degrees C-acclimated spot were more stable to heat than the 20 degrees and 15 degrees C-acclimated fishes.