title: Temperature and enzyme activity in poikilotherms. Isocitrate dehydrogenases in rainbow-trout liver.
abstract: 1. The kinetics of the thermally induced enzyme variants of the supernatant NADP-isocitrate dehydrogenase from rainbow-trout liver are investigated. 2. Fish acclimatized to 2 degrees C (cold-adapted enzyme) and 17 degrees C (warm-adapted enzyme) show different relative distributions of the three NADP-isocitrate dehydrogenase isoenzymes; this has been demonstrated with electrophoresis and electrofocusing techniques. 3. Plots of K(m) versus temperature for the cold-adapted and warm-adapted enzyme variants are complex in nature with apparent maximal enzyme-substrate affinity corresponding to the temperature at which the trout is acclimatized. Both substrates, dl-isocitrate and NADP(+), give similar curves although the magnitude of the K(m) change with temperature is much decreased in the case of NADP(+). 4. E(a) values of approx. 18kcal/mol were determined for both the cold-adapted and warm-adapted enzyme variants. 5. In an attempt to determine how velocities can be increased at low temperatures, cation, pH requirements, metabolite and enzyme concentrations were examined. 6. NAD-isocitrate dehydrogenase could not be detected in trout tissues.
mesh_terms: D000064:Acclimatization; D000818:Animals; D002848:Chromatography, DEAE-Cellulose; D003080:Cold Temperature; D004586:Electrophoresis; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007521:Isocitrate Dehydrogenase / Q000378:metabolism*; D007523:Isocitrates / Q000378:metabolism; D007525:Isoelectric Focusing; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D009249:NADP; D012487:Salmonidae / Q000378:metabolism*; D013696:Temperature
chemical_list: D007523:Isocitrates; D007527:Isoenzymes; D009249:NADP; D007521:Isocitrate Dehydrogenase