Factors affecting the assay of histone H1 and polylysine by binding of Coomassie blue G.

Although a mixture of calf thymus histones or the H2B and H4 fractions gave values in the Bradford assay that were similar to those for bovine serum albumin, low values were obtained with histone H1 and polylysine. The assay was found to be more sensitive for histone H1 and polylysine if the phosphoric acid concentration in the reagent was decreased or the polypeptide solutions contained low concentrations of nonionic detergents. Substitution of perchloric acid or hydrochloric acid for phosphoric acid and alcohol in the Coomassie blue G reagent provided an assay that was similar in sensitivity for histone H1 and a total histone mixture. It was suggested that the degree of metachromasia with Coomassie blue G may serve as a probe of conformational changes in histone H1.