Kynurenine-2-oxoglutarate aminotransferase (kynurenine specific, designated here KAT-II) and kynurenine pyruvate aminotransferase (designated here KAT-I) activities were detected in the kidney using 2 microM kynurenine. The major activities were performed by KAT-II and the contributi-n of KAT-I is about 1/15. KAT-I activity was detected in all organs tested. The liver showed the highest KAT-I activity, however, the highest activity of glutamine transaminase-K (GTK) was detected in the kidney. KAT-I activity was well corresponded with GTK activity in all organs except liver. KAT-I or GTK activity of crude extract didn't inhibited by addition of glutamine either kynurenine. KAT-I or GTK activity of purified preparation, however, inhibited strongly addition of glutamine either kynurenine. KAT-I and GTK showed different pH optimum profile, but purified and crude preparation of those were similar. Phenylpyruvate or 2-oxo-4-methiolbutyrate reduced the inhibition of purified KAT-I activity by glutamine using 2 microM kynurenine. Phenylpyruvate changed the Km value for kynurenine and Vmax, suggesting conformational change of the enzyme.