Deamination of L-Thyroxine by Oxidase and Transaminase of Rat Kidney Mitochondria

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Abstract
Two soluble enzyme preparations, one which effects oxidative deamination of thyroxine and another which catalyzes transamination between thyroxine and a-ketoglutarate in the presence of pyridoxal phosphate, have been obtained from extracts of rat kidney mitochondria disintegrated by sonic treatment. After successive fractionation of the extracts with ammonium sulfate, the oxidase and the transaminase activities were largely concentrated in precipitates obtained with 33–50 and 50–70 % ammonium sulfate, respectively. These oxidase and transaminase activities appear to be maximal at a pH of approximately 8.0 and 6.5, respectively.