Characterization of the major forms of human calcitonin in tissue and serum.

Abstract

We have characterized the major forms of immunoreactive calcitonin (i–hCT) in extracts of bothcancerous (thyroid and metastatic lymph node) and normal tissue (thyroid) and in serum from patients with medullary carcinoma of the thyroid (MCT). Samples were examined by isoelectric focusing with and without urea pretreatment. Affinity of the major calcitonin forms for both mannose– and N-acetylneuraminic acidspecific lectins was examined. Molecular weight of the major calcitonin forms was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Results of our investigation indicate that 1) the major forms of i–hCT in tissue extracts have apparent isoelectric points (pI) at pH ≤ 3.0, 5.0–5.5, 6.4–6.7, and 7.5–7.8; 2) the pI ≤ 3.0, 5.0–5.5, and 6.4–6.7 forms of calcitonin predominate in MCT serum; 3) pretreatment of both tissue extracts and MCT serum with urea, to reduceaggregation and protein binding, produced a 3– to 10– fold increase in detectable calcitonin; 4) when frozen at their pi, the m...