A conformational change in bovine beta-lactoglobulin at low pH.

A conformational change at low pH in bovine beta-lactoglobulin A has been studied by intrinsic fluorescence and fluorescence of the bound dye 8-anilinonaphthalene-1-sulphonate. Both studies show that when the pH of beta-lactoglobulin solutions is altered between 6.5 and 2.0, a rapid change in protein conformation occurs, followed by a slower conformational change. It seems likely that the rapid changes are linked with the predominance of protein dimer at pH 6.5 and monomer at pH 2.0. The slow changes involve shifts in protein conformation of the region that includes one of the protein tryptophan residues.