THE METABOLIC INTERRELATIONS OF THYROXINE AND DIIODOTYROSINE IN THE THYROID GLAND AS SHOWN BY A STUDY OF THEIR SPECIFIC ACTIVITY-TIME RELATIONS IN RATS INJECTED WITH RADIOACTIVE IODINE

The evidence in support of the hypothesis that thyroxine is formed in the thyroid from tyrosine with diiodotyrosine as an intermediate has recently been reviewed by Harington (1). The presence of relatively large amounts of diiodotyrosine in the thyroid gland and, in particular, t,he finding that natural thyroxine and natural tyrosine are configuratively related are considered by hii to favor strongly such a mechanism. Further support is offered by the isolation of thyroxine from iodinated proteins (2-4) and by the finding that thyroxine is formed during the prolonged incubation of diiodotyrosine in a slightly alkaline solution (5-10).