Colorimetric determination of serum isocitric dehydrogenase. Comparison with a spectrophotometric procedure.

ISOCITRIC DEHYDROGENASE (lCD)5 is one of the newer enzymes that has recently come to the attention of clinical medicine. Sterkel et at. (1) have shown that serum lCD is elevated in hepatitis and to a lesser extent in some malignancies. Bowers and McDuffee (2) observed marked elevations of serum lCD in 2 patients who at autopsy showed extensive central lobular liver cell necrosis. The enzyme activity in animal tissue is known to be triphosphopyridine nucleotide (TPN)-linked (3) and requires Mn as an activator. Wolfson and Williams-Ashman (4) found that these conditions also prevail in the analysis of serum lCD. The conversion of isocitric acid (ICA) to -ketoglutaric acid (KGA) and CO2 is assumed to take place through the enzymatic dehydrogenation to oxalosuccinic acid: