Biochemical studies in marine species--I. NADP(+)-dependent isocitrate dehydrogenase from turbot liver (Scophthalmus maximus L.).
1. An NADP+-dependent isocitrate dehydrogenase was extracted from turbot liver. The enzyme required divalent cations (Mg2+ or Mn2+) for its activity but was inhibited by high salt concentrations. 2. The enzyme had an optimum activity in the pH range between 7.5 and 9.0. The enzymic activity increased with temperature (in the range of 5 to 68 degrees C) with an Ea of 23.5 kJ/mol and a Q10 of 1.34. 3. The apparent Km values for the substrates were 6.5 microM for NADP+, 56 microM for Mg2+, 87 microM for Mn2+ and 4.2 and 73.5 microM for the complexes Mg-isocitrate and Mn-isocitrate, respectively. The physiological significance of these results is discussed. 4. The enzyme was inhibited by citrate and adenine nucleotides. The degree of inhibition depended on the relation between the concentrations and that of magnesium. A possible regulating mechanism is proposed.
Munilla-Morán
R
R
Department of Brewing and Biological Sciences, Heriot-Watt University, Edinburgh, Scotland.
Stark
J R
JR
D000227:Adenine Nucleotides / Q000494:pharmacology; D000818:Animals; D002951:Citrates / Q000494:pharmacology; D005412:Flatfishes / Q000378:metabolism*; D006597:Fructose-Bisphosphatase / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007521:Isocitrate Dehydrogenase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007656:Ketoglutaric Acids / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008274:Magnesium / Q000378:metabolism; D008345:Manganese / Q000378:metabolism; D013379:Substrate Specificity; D013696:Temperature
D000227:Adenine Nucleotides; D002951:Citrates; D007656:Ketoglutaric Acids; D008345:Manganese; D007521:Isocitrate Dehydrogenase; C039355:isocitrate dehydrogenase (NADP+); D006597:Fructose-Bisphosphatase; D008274:Magnesium