Kynurenine transaminase activity in rat liver was found in both the mitochondrial and supernatant fractions. The mitochondrial and supernatant fractions contained ( a ) kynurenine–pyruvate transaminase, which showed a preference for pyruvate as amino acceptor and a pH optimum between 8.0 and 8.5, and ( b ) kynurenine–α-oxoglutarate transaminase, with a preference for α-oxoglutarate and a pH optimum between 6.0 and 6.5. Possible roles of these enzymes in tryptophan metabolism in the liver are discussed.
The transamination of aromatic l -amino acids (5-hydroxytryptophan, tryptophan, tyrosine, phenylalanine and kynurenine) was shown to be catalysed by enzyme preparations from rat small intestine. On the basis of the partial purification and characterization of these aromatic amino acid transaminases, it is suggested that rat small intestine contains several kinds of aromatic amino acid transaminases.