Adsorption of parathyrin: pitfall for solid phase assays using radiolabelled antibodies?

The physicochemical behaviour of parathyrin on surfaces was investigated. Parathyrin is bound to the wall of polyethylene, polypropylene and flint glass tubes. This adsorptive binding of the hormone, detected by labelled antibodies, is a time-dependent process which is complete within one hour. The addition of plasma decreases but does not prevent adsorption. Coating of the tubes with an anti-N-regional or anti-C-regional antiserum decreases the sensitivity of the detection of 1-34, 53-84 and 1-84 intact parathyrin, when performed in buffer. In the presence of plasma the increase of radiolabelled antibody detecting the parathyrin was more pronounced when tubes were precoated with an anti-parathyrin antibody. The sensitivity of the 1-84 parathyrin assay was also reduced when incubation was carried out in the presence of high concentrations of parathyrin-fragments, calcitonin, somatostatin or bovine serum albumin. Assay specificity seems to be related to the specificity of the labelled antibody for the respective hormonal fragment, not to that of the antibody used for coating the tubes. This investigation illustrates the necessity for the careful control of parathyrin assay conditions, e. g. non-specific binding of native parathyrin and radiolabelled tracers to laboratory reaction vessels.