Radioimmunoassay for the antifreeze polypeptides of the winter flounder: seasonal profile and immunological cross-reactivity with other fish antifreezes.

The polymerization of winter flounder antifreeze polypeptide (AFP) with glutaraldehyde to increase its antigenicity and the conjugation of the AFP to bovine serum albumin so that the AFP could carry a radioiodine label have allowed the development of a convenient and reliable radioimmunoassay (RIA) for the antifreeze. A seasonal concentration profile of serum AFP as determined by the RIA corresponded closely with its activity profile. Winter serum concentrations of AFP measured by the RIA (7-11 mg/mL) agreed well with antifreeze recovery from Sephadex G-75 chromatography of serum (6-10 mg/mL), but less so with concentration estimates reported from activity measurements (12-25 mg/mL) (Petzel, D. H., Reisman, H. M. & DeVries, A. L. (1980) J. Exp. Zool. 211, 63-69). A small but measurable immunological cross-reactivity was detected between the antiflounder AFP and other fish antifreeze polypeptides. Such cross-reactivity was quite unexpected considering the large compositional and structural differences among the various AFP and its significance remains unclear.