Collagen and histone H1 are stained a pink-red color with Coomassie Brilliant Blue R-250 (Coomassie R) instead of the blue color of most proteins after SDS-PAGE. Spectrophotometrically, this metachromasia was characterized by an increase in the absorbance at 535 nm and a decrease in the absorbance at 600 nm. The ratio of the absorbance at 535 nm to that at 600 nm ranged from 1.5 to 2.5 for the pink-red-stained proteins and was about 1 for the blue stained proteins. In their amino acid composition, the pink-red-stained proteins collagen and histone H1 contained less than 11% of hydrophobic amino acid residues, whereas the five blue-stained proteins examined contained more than 25% of such residues. Collagen and histone H1 also induce circular dichroism (CD) of Coomassie R in the visible region with a different CD spectrum. In the case of native collagen, a CD (+) band at 530 nm with 10(5) molar ellipticity was observed, while the denatured collagen showed a CD(-) band at 530 nm. When the amino groups of the amino acid residues in collagen and histone H1 were converted into hydrophobic groups by fluorescamine treatment, these proteins stained bluer than pink-red and the induced CD was a lower intensity. This is the first report of the metachromatic interaction between a protein and Coomassie R that is accompanied by CD induction. This report also suggests that the induction of metachromasia and CD of Coomassie R was due to the low content of hydrophobic amino acid residues in the peptides.