Effects of temperature on the respiration rates and the kinetics of citrate synthase in two species of Idotea (Isopoda, Crustacea)

The two species of isopods, Idotea baltica (Pallas) and Idotea emarginata ( Fabricius), co-occur frequently near Helgoland, North Sea, occupying differ ent ecological niches. Respiration rates and kinetic properties of citrate synthase (CS) were compared in these species in order to identify possible mechanisms of temperature adaptation. Specimens were acclimated to 5 and 15 degrees C prior to further investigations. Respiration rates were measured under normoxic conditions at 5, 10 and 15 degrees C. CS was partly purifie d chromatographically and influences of temperature, pH, substrate saturati on and ATP-concentration on enzyme activity were examined. In both species, rising temperatures led to linearly increasing oxygen consumption, with es timated Q(10) values between 3.2 and 4.2. Only I. baltica showed an effect of short term acclimation: warm adapted animals had always higher respirati on rates than cold adapted ones. In I. emarginata, the acclimation temperat ure had no effect on oxygen consumption. Furthermore, its CS slightly indic ates higher affinity to oxaloacetic acid when specimens were adapted to 15 degrees C compared to those maintained at 5 degrees C. Any effect of the ex perimental temperature on CS in I. baltica was negligible. The results are discussed in view of the different habitats occupied by the species compare d. (C) 2000 Elsevier Science Inc. All rights reserved.