Abstract

Iodine metabolism in minced beef thyroid was altered by 10^-3 to 10^-5 M dinitrophenol. I¹³¹ uptake was decreased. However, relatively normal amounts of that iodine which had been taken up were found as monoiodotyrosine. Halogenation of this compound to give diiodotyrosine appeared to be blocked by dinitrophenol. Low concentration of diiodotyrosine was neither the result of stimulated release of iodotyrosines from the thyroid nor related to the pool of available iodine. In 10^-3 and 10^-4 M dinitrophenol normal thyroid responses to thyrotropin, i.e., increased iodine uptake and diiodotyrosine synthesis were not seen.