ASSAY OF ORNITHINE AMINOTRANSFERASE WITH NINHYDRIN

We developed an assay system for ornithine amino-transferase (EC 2.6.1 .13) using ninhydrin. Pyrroline 5-carboxylate, a product of enzymatic transamination, reacts with ninhydrin under hot acidic conditions to f orm a reddish pigment soluble in ethanol. The millimolar extinction co efficient of reaction product dissolved in ethanol was 16.5 at 510 nm. Acidification with perchloric acid effectively abolished the interfer ing color development by L-ornithine and L-glutamate. The paired activ ity measurement in mouse tissues by ninhydrin and o-aminobenzaldehyde methods showed a good correlation (gamma = 0.985). In our ninhydrin me thod, stable ninhydrin replaced unstable o-aminobenzaldehyde, and sens itivity was much higher than that with the conventional o-aminobenzald ehyde method. (C) 1994 Academic Press, Inc.