Abstract
The structure of thyroxin as recently determined by Harrington 1 represents the substance as a derivative of di-iodotyrosine and as containing two benzene rings. It is, therefore, of some interest to know what effect, if any, other derivatives of di-iodotyrosine containing two aromatic nuclei, would exert on basal metabolism.
Two such substances have been examined, namely, di-iodotyrosyl-di-iodotyrosine and the cyclic anhydride (diketopiperazine) of di-iodotyrosine. The former substance may be prepared by the action of iodine in feebly alkaline solution upon tyrosyl-tyrosine, or by the regulated action of alkali on the cyclic anhydride of di-iodotyrosine. The latter substances cannot be obtained by the direct action of iodine upon tyrosine anhydride, but may be readily attained by the action of iodine chloride in acetic acid upon the anhydride. Both substances are cream colored microcrystallin compounds, which in their solubilities and general chemical deportment, colour reactions, etc., show considerable resemblance to thyroxin. The anhydride of di-iodotyrosine melts at about 245 to 250 degrees (uncorr.) while di-iodotyrosyl-di-iodotyrosine does not melt sharply but begins to decompose above 200 degrees. The substances were prepared for these experiments by H. D. Dakin.
The metabolism experiments were carried out on a normal male individual of about 101 kilos, 184.5 cm. in height. All determinations were done in triplicate under basal conditions, either the Tissot or Benedict machine being used. All Substances investigated were taken intravenously.
Basal metabolic rates determined on five days during the week preceding the injection of the cyclic anhydride of di-iodotyrosine varied between −9 and −12 per cent. Twenty-four hours after the injection of 21 mg. of the substance the basal rate was −9 per cent, and at the end of 48 hours was −7 per cent.
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