Differential spectrophotometry of iodoamino acids and iodinated proteins. Aqueous ethylene glycol solutions of iodotyrosines, thyroxine and thyroglobulin.

Solvent perturbation difference spectra and corresponding molar extinction coefficients of solutions of monoiodotyrosine, diiodotyrosine and thyroxine with protonated and deprotonated hydroxyls were measured with 20% ethylene glycol as perturbant. Data obtained were applicable to the development of the method of quantitative estimation of the number of iodotyrosine and thyroxine residues accessible to ethylene glycol in iodinated proteins. This method was used for the determination of iodoamino acids available to ethylene glycol in bovine thyroglobulin (naturally iodinated protein).