Adaptation of Drosophila enzymes to temperature—VI. Acclimation studies using the malate dehydrogenase (MDH) and lactate dehydrogenase (LDH) systems

A~tract--l. Thermal acclimation response was studied in several tropical and temperate Drosophila species (temperate: D. virilis, D. americana; tropical: D. arizonensis, D. willistoni), as well as in the sibling species D. simulans, D. mauritiana and their interspecific hybrid masi. All these species were allowed to grow at 14, 25 or 28°C for one generation. 2. Temperature dependent catalytic properties (K m, Ks, specific activity, V~/K~ADK=) were detected at 25°C, in three enzymic systems [lactate dehydrogenase (LDH), cytosolic malate dehydrogenase (cMDH), and mitochondrial malate dehydrogenase (mMDH)] and two developmental stages. 3. Some convergences between LDH catalytic properties (K~ A°, specific activity, Vm~/K~^°K=t~') and thermal habitat of temperate and tropical species were revealed, and thus suggested that temperature has played a selective role in shaping these properties. 4. Other differential thermal acclimation responses, found between homologous enzymes (MDH or LDH), could be also considered as additive components which contribute to the pool of variability that can serve as the material for selective compensation to temperature, where the ontogenetic stage seems also to be involved. 5. For the most of the catalytic constants studied in the sibling species (D. mauritiana, D. simulans) and their hybrid masi, middle acclimation temperatures minimizes the differences among the strains, while extreme temperatures maximizes them. 6. Cytosolic and mitochondrial MDH, which participate in the same biochemical cycle but act in the cytosol and mitochondria respectively, do not react coordinately to thermal acclimation. Key Word Index--Adaptation; acclimation; Drosophila; enzymes; enzyme kinetics; malate dehydrogenase; lactate dehydrogenase; development.