The Metabolic Fate of Isotopically Labelled Proteins, Azoproteins and Azohaptens

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Abstract
Summary: Sulfanilic acid as well as sulfanilazodyes, prepared by coupling diazotized S35-sulfanilic acid with tyrosine, histidine and phenol, were injected into rabbits. A small but significant amount of the injected activity was bound to the proteins of the blood and the tissues. The protein-bound radioactivity, 8–13 days after injection, was about 10 times lower than after the injection of equivalent amounts of sulfanilazoproteins. In the liver homogenate, most of the protein-bound azodye was present in the large cytoplasmic granules (mitochondrial fraction). When sulfanilazotyrosine was added in vitro to the liver homogenate, it was not bound to the proteins of the cytoplasmic granules. Rabbit serum γ-globulin (RGG), beef serum γ-globulin (BGG) and ovalbumin (OA) were coupled with traces or with large amounts of S35-sulfanilic acid. The heavily labelled sulfanilazoproteins were rapidly eliminated from the circulation and deposited in the organs in the same manner as heavily labelled iodoproteins. Trace-labelled OA behaved similarly, whereas trace-labelled RGG circulated in the blood for a long time without significant deposition in the organs. Trace-labelled BGG circulated in the blood over a period of four to seven days, after which time it was eliminated and deposited in the organs.