Radioimmunoassay of sheep alpha- and gamma-crystallins I. 125I labelling of sheep gamma-crystallin. Characterization of the assays in detecting homologous and heterologous lens crystallins

A radioimmunoassay for sheep γ-crystallin is described. ¹²⁵I labelling of native γ-crystallin is difficult to accomplish, probably due to its high thiol content but after alkylation labelling became satisfactory. Gamma crystallin tends to form complexes with α-crystallin, making it difficult to obtain a pure α-crystallin preparation. The described immunoassay is specific for γ-crystallin and is not influenced by the presence of other lens crystallins. The lower limit of sensitivity of the assay is 2 ng/ml. The assay is compared to the previously described assay for α-crystallin. The assays were used to evaluate cross reactions between α- and γ-crystallins from four different species.