High-resolution 1H-NMR spectroscopy at 600 MHz has been used to investigate the conformational transitions of the histidine-binding protein J of Salmonella typhimurium in solution as a function of pH and of L-histidine concentration. The dissociation constant for the binding of L-histidine to histidine-binding protein J increases from 6.0 X 10(-8) to 5.1 X 10(-7) M in going from pH 5.57 to 8.00. The conformation of this protein as observed by 1H-NMR also changes over this range of pH. However, when L-histidine is bound, the changes in conformation with pH are much smaller. Also, the pK for the single histidyl residue in histidine-binding protein J changes from 6.75 in the absence of L-histidine to 6.52 when L-histidine is bound. Earlier work in this laboratory resulted in the identification of several proton resonances believed to be at or near the L-histidine-binding site. Two of these resonances have been assigned to a tyrosine and the single histidyl residue in the histidine-binding protein J molecule.