The kidney was reported to be the main site of parathyroid hormone inactivation in rats (Orimo et al., 1 965a). Such inactivation is apparently carried out by some heat labile, pH dependent principle inhibited by proteinase inhibitors (Orimo et al., 1965b). Vajda et al. (1969) introduced the use of 125 I-labeled parathormone in studies on the hydrolysis of this hormone. Martin et al.(1969) demonstrated degradation of 125 I-labeled parathormone by a rat kidney enzyme. Since the nature of such enzyme(s) which are responsible for parathormone degradation still remains obscure, we have studied the optimum pH, organ and subcellular distribution, substrate specificity, and effect of various enzyme inhibitors and metal ions in order to define the mechanism of such degradation more precisely.

The kidney plays a key role in parathyroid hormone degradation, with a heat-labile, pH-dependent enzyme responsible for the process, and various inhibitors and metal ions affecting this process.

Enzymatic hydrolysis of 125I-labeled parathyroid hormone.

Key Takeaway: The kidney plays a key role in parathyroid hormone degradation, with a heat-labile, pH-dependent enzyme responsible for the process, and various inhibitors and metal ions affecting this process.