Abstract
The cytosolic fraction of porcine thyroid, liver, kidney and brain tissue contains proteolytic activity capable of calcitonin degradation into peptide fragments. The degree and pattern of calcitonin fragmentation produced by the tissue examined in this study were determined by subjecting aliquots of incubation media to gel filtration chromatography immediately after incubation. Thyroid cytosol produced calcitonin fragmentation in a time-dependent manner. Fragmentation produced by liver, kidney and brain appeared to be quantitatively and qualitatively different from that produced by the thyroid. Hormone degradation produced by thyroid cytosol was substantially inhibited by p-hydroxymercuribenzoate, thimerosal and iodoacetamide but not by pepstatin. The thyroid cytosolic peptidase may be involved in calcitonin turnover and presecretory regulation within the "C' cell. Further, fragmentation within the thyroid may be responsible for the multiple immunoreactive forms of calcitonin which have been detected in the circulation.
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