Kynurenine aminotransferase and alpha-aminoadipate aminotransferase: III. Evidence for identity with halogenated tyrosine aminotransferase.

A nearly homogeneous preparation of α-aminoadipate (kynurenine) aminotransferase exhibited substantial activity with 3,5-diiodo-L-tyrosine, a major substrate for halogenated tyrosine aminotransferase. The new activity was found, according to heat inactivation and several inhibition studies, not to be attributable to contamination. Many of the properties previously reported for the two enzymes are identical or very similar. This paper lists these similarities and reports our observations of additional similarities of these activities in the supernatant and mitochondrial fractions of both rat kidney and liver. The properties of the purified enzyme and the noted similarities suggest that α-aminoadipate aminotransferase, kynurenine aminotransferase, and halogenated tyrosine aminotransferase activities are associated with the same protein. These activities are discussed in terms of a possible role in thyroid hormone metabolism.