Inactivation of Porcine Calcitonin by Rat Kidney Microsome

Biological activity of porcine calcitonin was most actively inactivated by the rat kidney homogenate than by other tissue homogenates. Among the various subcellular fractions of the rat kidney homogenate examined, microsome fraction was most active in the in vitro inactivation of porcine calcitonin. Inactivation of porcine calcitonin by the rat kidney microsome was dependent on pH and temperature. Inactivating activity of the rat kidney microsome was inhibited by 1 X 10(-3) M monoiodoacetate and 1 X10(-5) M p-chloromercuribenzoate. These results suggest that porcine calcitonin is probably inactivated by a SH-enzyme in the rat kidney microsomes. However, the participation of other enzymes cannot be ruled out, since the inactivating activity of the rat kidney microsome fraction is also inhibited by 1 X 10(-4) M diisopropylfuorophosphate.