EVIDENCE FOR THYROCALCITONIN BINDING TO PROTEIN IN PLASMA

Abstract
SUMMARY A simple method is described for concentrating thyrocalcitonin from plasma by adsorption onto finely divided silica gel. An approximately 20-fold increase in biological activity with respect to protein content has been obtained with recoveries of added material of about 80%, allowing subsequent fractionation and bioassay of the fractions. Porcine thyrocalcitonin was added to either porcine or human plasma to give concentrations within the range observed in porcine thyroid venous plasma. Concentration on silica gel followed by gel filtration on Sephadex G 50 resulted in separation of the biological activity into two fractions, one of which was associated with the plasma proteins. A similar result was obtained with porcine thyroid venous plasma containing endogenous thyrocalcitonin. Preparative ultracentrifugation of plasma rich in thyrocalcitonin also provided evidence suggestive of some protein binding of the hormone. It is concluded that thyrocalcitonin is carried in plasma partly free and partly bound to plasma protein.

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