Heterogeneity of rat thyroglobulin labelled with 131I in vivo

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Abstract
The rates of release of mono- and di-[I131]-iodotyrosine during autolysis of homogenates of rat thyroid labelled for 0.5, 1, 2, 18 and 48 hours in vivo studied atpH 3.6. In all the experiments both the [I131]iodotyrosines were released from thyroglobulin at equal rates at the same times of labelling. The rates of release of the [Il31]iodotyrosines were greatest at the shortest time of labelling, and decreased as the time of labelling was increased. In glands labelledfor 0.5 to 4 hours, but not for 18 hours or longer, free mono- and di-[I131]iodotyrosine appeared rapidly in the autolysates. The rate of autolysis of rat-thyroid homogenates was about 10 times as great at pH 3.6 as at pH 5.6. Preliminary acid denaturation of the substrate enhanced the rate of autolysis at pH 5.6.