A new method of iodinating collagens for use in radioimmunoassay.

Purified collagens from a variety of species were iodinated to a high specific activity with the N-hydroxysuccinimide ester of I¹²⁵-labeled p-hydroxyphenyl propionic acid (Bolton-Hunter reagent). Labeling had no effect on the immunoreactivity of the collagen as determined by hemagglutination inhibition. This compound presumably acylates the abundant ?-amino groups of lysyl and hydroxylysyl residues in the collagen molecule. Using this method it is possible to label pepsin-extracted collagen from which the terminal nonhelical extensions containing tyrosine have been cleaved. The application of Bolton-Hunter-labeled collagens to radioimmunoassay of affinity-purfied antibodies against collagen is demonstrated.