Purification and characterization of the periplasmic lysine-, arginine-, ornithine-binding protein (LAO) from Salmonella typhimurium.

The lysine-, arginine-, ornithine-binding protein (LAO) from Salmonella typhimurium has been purified to homogeneity and characterized. The dissociation constants (KD) were determined by equilibrium dialysis assay to be 14, 15, and 29 nM for L-arginine, L-lysine, and L-ornithine respectively. L-Histidine was found to be a relatively good ligand (KD, 500 nM). Methods have been developed for the separation of liganded from unliganded LAO, for the estimation of bound ligand, and for unliganding LAO. Liganded and unliganded LAO are shown to have distinct UV spectra. The UV spectrum also varies with the nature of the substrate. Inhibition studies with substrate analogs yielded information useful for understanding the nature of the ligand-binding pocket.