STRUCTURAL CHARACTERIZATION OF CYTOSOLIC NADP(-DEPENDENT ISOCITRATE DEHYDROGENASE FROM RAT OVARY())

Cytosolic NADP(+)-dependent isocitrate dehydrogenase was purified to h omogeneity from superovulated rat ovaries. Amino acid sequence informa tion was obtained by analyzing peptides generated by digestion with ei ther cyanogen bromide or trypsin. Eleven peptides were sequenced and a total of 146 amino acids were identified. Nine of these peptides were found to be 60-100% identical with sequences from mitochondrial NADP( +)-dependent isocitrate dehydrogenase. Conservation of amino acids was observed for residues that were previously identified as potentially binding isocitrate-Mg2+. Circular dichroism measurements showed that t he structure is composed of approximately 35% alpha-helix and 21% beta -sheet segments. Temperature denaturation studies indicated that the e nzyme is more stable in the presence of isocitrate.