Location of naphthol yellow-S binding site on bovine serum albumin.

The characteristics of the binding site in the first binding class of naphthol yellow-S (NY-S) on bovine serum albumin (BSA) were studied. The binding of NY-S to BSA at an equimolar ratio of each material resulted in a marked quenching of intrinsic fluorescence of BSA and a decrease in the binding capacity of 1-anilinonaphthalene-8-sulfonate to BSA. The binding of NY-S to BSA was diminished by the chemical modification of tryptophan residue in the BSA molecule with 2-hydroxy-5-nitrobenzyl bromide and o-nitrophenylsulfenyl chloride. The higher modifications rate of tryptophan residue decreased the binding constant of NY-S to BSA. These results suggest that the first binding site of NY-S to BSA is located in a hydrophobic area including tryptophan which is position 134 on the amino acid sequence of BSA. Studies on BSA modified with diethylpyrocarbonate demonstrated that a histidine residue also may participate in the binding of NY-S to BSA.