Studies of Thyrocalcitonin Inactivation in Vitro ∗

Summary

A preparation of porcine TC containing about 12 MRC U/mg solids was found to lose all hypocalcemic activity when incubated in 0.1 M Tris buffer, pH 7.5, for 30 min at 23 °. Crude TC preparations (0.03 U/mg or 0.12 U/mg) did not lose hypocalcemic activity under these conditions. Inactivation of TC was found to be pH dependent with little or no loss of activity occurring at pH 5 or below. Both normal serum and serum heated at 60 ° for 20 min decreased TC inactivation which occurred above pH 5.0, when added to the medium at a concentration of 0.1-1.0%. High concentrations of normal serum, however, inactivated TC. Of several agents utilized, in attempts to prevent the loss of hypocalcemic activity which occurred in vitro at neutral pH, porcine albumin and egg albumin (but not bovine or human albumin) were found effective to an extent similar to that found with serum.