Absorption loss of peptides to the plastic tube in radioreceptor assay of calcitonin and beta-endorphin: protection by detergents.

During development of the calcitonin binding assay using rat brain particulate fraction, it was noticed that 125l-salmon calcitonin-l (125-SCT) was partly absorbed by the polypropylene tube surface in an irreversible manner. Absorption was partially prevented by cold SCT and complete prevention was achieved by bacitracin. Triton X-100, Brij 36T, and some Zwittergents in such concentration ranges which appeared not to disrupt the 125l-SCT binding ability of brain tissue. The brain fraction itself exhibited a similar preventive effect. The anti-absorbing effect of Brij 36T was also observed in an opiate receptor binding assay for beta-endorphin. These results led us to recommend that the binding assay for these peptides should be done only in the presence of an appropriate anti-absorbant.