Purification and comparative properties of isoenzymes of nicotinamide–adenine dinucleotide phosphate–isocitrate dehydrogenase from rat heart and liver

Abstract

1. Rat liver and heart major isoenzymes of NADP-isocitrate dehydrogenase have each been purified about 100-fold by a combination of ammonium sulphate fractionation and chromatography on ion-exchange cellulose and their properties compared. 2. The properties were similar in respect of pH, inhibition by Hg(2+) and Michaelis constants for isocitrate and NADP. 3. Some of the properties of the isoenzymes were different. 4. The heart isoenzyme was activated about 210% by 0.8m-ammonium sulphate whereas the liver isoenzyme was unaffected. The heart isoenzyme showed greater sensitivity to inactivation by heat (30 degrees C for 30min), whereas the liver isoenzyme was more sensitive to inactivation by p-chloromercuribenzoate and by Cu(2+). 5. The Michaelis constants with 3-acetylpyridine-adenine dinucleotide phosphate showed a twofold difference between liver and heart isoenzyme. 6. The differential sensitivity to heat and its mainly non-cytoplasmic location may be an explanation of the failure of plasma isocitrate dehydrogenase activity to increase after a myocardial infarction.

A comparison of the soluble and mitochondrial forms of human isocitrate dehydrogenase and an examination of the secondary isozymes derived from the soluble form

“…Michaelis constants for the human enzymes were in the micromolar range and are similar to those reported for the mitochondrial and soluble enzymes from other species (Higashi et al 1965, Islam, Bell & The two forms of the enzyme were found to differ in thermostability, the soluble form being considerably more stable than the mitochondrial. This is in agreement with the results obtained for the enzymes from rat heart and liver (Islam et al 1972). Examination of the electrophoretic properties of ICD in different human tissues revealed considerable variation.…”

Regulation of mitochondrial NADP-isocitrate dehydrogenase in rat heart during ischemia

“…Using a NIH3T3 cell line, Jo et al [15] showed that mitochondrial NADP-ICDH acted as an antioxidative enzyme. The two NADP-ICDH isoenzymes in mammalian tissues were shown to differ in their distribution, sub-cellular localisation and some molecular and catalytic properties [16][17][18][19]. Earlier we reported the properties of the ischemic cytoplasmic NADP-ICDH from a rat heart and showed that enzyme could serve as an alternative to the pentose phosphate pathway as a source of NADPH at pathology [20].…”