The Fate in Rats of Internally and Externally Labelled Heterologous Proteins

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Abstract
Summary: S35 serum proteins, produced by the incorporation of S35 amino acids in vivo were coupled with traces of I131 in vitro. The persistence of the doubly labelled heterologous proteins in rat livers and their subcellular distribution was studied. In terms of per cent of administered activity, during the time period studied, a greater amount of radiosulfur than radioiodine persisted. Nine days after the injection of the doubly labelled proteins the radiosulfur was more evenly distributed among the subcellular fractions of the liver than the radioiodine. Similar distribution and persistence of S35 in the liver proteins was found when iodine-free serum albumin containing S35 amino acids was injected. An interpretation for the different fate of the two isotopic labels is given.