Kynurenine transaminase of rat kidney; a study of coenzyme dissociation.

Cell-free extracts of rat kidney catalyze the conversion of kynurenine to kynurenic acid by means of a transamination reaction (2). Such extracts lose kynurenine transaminase activity rapidly when added to phosphate buffer solutions with pH below 7 unless ol-ketoglutarate is added (2). Further studies in this laboratory have shown that this inactivation is completely reversed by the addition of small amounts of pyridoxal phosphate or pyridoxamine phosphate. This observation suggests that inactivation results from dissociation of one or both of these coenzymes from the apotransaminase and that a-ketoglutarate prevents this dissociation. The present report seeks to describe this association-dissociation phenomenon and to explain the protective action of or-ketoglutarate.