The kynurenine transaminase of rat kidney.

The conversion of kynurenine to kynurenic acid was observed in intact animals by Kotake (2) in 1931. This reaction was studied in vitro by Mason and Berg (3, 4), who observed that slices and homogenates of rat liver converted both tryptophan and kynurenine to kynurenic acid. Similar preparations from rat kidney did not convert tryptophan to kynurenine or kynurenic acid, but had a somewhat greater activity than liver in the conversion of kynurenine to kynurenic acid (3, 4). Liver and kidney preparations from pyridoxine-deficient rats showed a relatively weak action in the conversion of kynurenine to kynurenic acid and to anthranilic acid, but activity in both reactions was restored by the addition of pyridoxal phosphate to the incubation medium (4). On the basis of a requirement for pyridoxal phosphate and for a-ketoglutarate, it was suggested (4) that kynurenic acid is formed via a transaminstion reaction. It was recently demonstrated that tra.nsamination is the mechanism for its formation by extracts of Pseudomonas cells (5) and by the mitochondria of rat liver (6). The purpose of this paper is to report the presence of a kynurenine transaminase in rat kidney and to outline some of its properties.