Browning hydrophobic interactions

Another assay, the Bradford assay, also known as the Coomassie dye binding method, was first described in 1976 [19]. In an acidic environment, proteins will bind to Coomassie dye and cause a shift from the reddish brown color (465 nm) to the blue dye protein complex read at 595 nm. The development of the color is attributed to the presence of the basic amino acids arginine, lysine, and histidine. Van der Waals forces and hydrophobic interactions account for the dye binding and the number of Coomassie blue dye molecules bound is roughly proportional to the number of positive charges on the molecule. A protein molecular weight of about 3 kDA is required for successful color development. The Bradford assay dose response is nonlinear and this method demonstrates the greatest difference in reactivity with BSA compared to BGG. 

The metachromatic effect is presumably due to the association of the dye molecules on binding with the polyanion which may involve both electrostatic and hydrophobic interaction. The destruction of metachromatic effect may occur on addition of low molecular weight electrolytes, alcohols, or urea. The destruction of metachro-masy by alcohols and urea is attributed to the involvement of hydrophobic bonding, as has already been established (Browning and Holtzer, 1961 Frank and Evans, 1945 Frank and Quist, 1961 Kauzmznn et al, 1959 Mukherjee and Ray, 1963 ... 

Fig. 3.10. MOLCAD-predicted CB2-binding pocket surrounded by active amino acid residues, showing an amphipathic contour, hydrophilic center (blue), and hydrophobic cleft (brown). The site-directed mutagenesis-detected binding residues are color-coded in terms of their distance to the pocket (magenta > yellow > green > blue) as the interaction weakens. (See color plate.)...

Dacquirv J.-P., Cross, H.E., Brown, D.R., et aL, 2010. Interdependent lateral interactions, hydrophobicity and acid strength and their influence on the catalytic activity of nanoporous sulfonic add silicas. Green Chemistry 12, 1383-1391. 

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