Habener et al have described enzymatic inactivation of ovine calcitonin in bovine plasma. The in vitro effects of human plasma were studied on human calcitonin (HCT). As measured by immunoassay, HCT progressively disappears when incubated in human plasma, the loss being maximal at 37.5°C at pH 6.0 to 7.0. Under these conditions, in plasmas from 20 normal volunteers, an average of 19% of added HCT (500 ng/ml) was lost during 5 hr of incubation (range 0 - 38%) and 62% within 24 hr. (range 35 - 85%). When 125I HCT was incubated with human plasma, progressive formation of a labeled fragment of 125I HCT was demonstrated by chromatography of the incubates on BioGel P 10. In the most active plasmas, after 24 hr. incubation, 80 - 90% of initial radioactivity eluted as a labeled fragment. In studies with 125I HCT and unlabeled HCT in the same plasma, excellent correlation was seen between extent of fragment formation and loss of immunoreactive HCT. The labeled fragment was smaller in molecular weight than a labeled 1-17 amino acid fragment produced by tryptic digest of 125I HCT and was not bound by antisera recognizing amino acids 16-17 and 28-29. It is concluded that, in vitro, human plasma inactivates HCT by enzymatic degradation producing a fragment within the 1-15 amino acid portion of the molecule.
|Original language||English (US)|
|Number of pages||1|
|Issue number||3 (I)|
|State||Published - 1973|
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