Cytosolic NADP(+)-dependent isocitrate dehydrogenase. Isolation of rat cDNA and study of tissue-specific and developmental expression of mRNA.

Immunoscreening and DNA hybridization were used to isolate a 1.72-kilobase pair cDNA encoding cytosolic NADP(+)-dependent isocitrate dehydrogenase from a rat liver, lambda gt11 cDNA library. The identity of the cDNA was confirmed by comparison of the deduced amino acid sequence with sequences of peptides obtained from purified ovarian cytosolic isocitrate dehydrogenase. The 1.72-kilobase pair cDNA sequence translated into a protein of 414 amino acid residues with a molecular mass of 46,681 Da. The amino acid sequence contains a tripeptide (AKL) at the COOH terminus which represents a possible peroxisomal targeting sequence. The deduced amino acid sequence of the rat liver cytosolic isocitrate dehydrogenase showed 70 and 59% identity with sequences reported for NADP(+)-dependent isocitrate dehydrogenases from porcine mitochondria and yeast cytosol respectively. Northern blot analysis demonstrated a 13-fold increase in expression of cytosolic NADP(+)-dependent isocitrate dehydrogenase mRNA during the gonadotropin-induced development of the immature rat ovary. In comparative studies, the cytosolic and mitochondrial isocitrate dehydrogenase mRNAs were found to differ in size (2.2 and 1.8 kilobases, respectively) and to be differentially expressed in various tissues of the rat. Distinct digestion patterns were also obtained in Southern blot analysis of rat genomic DNA.