Purification and Characterization of a Histidine-binding Protein from Salmonella typhimurium LT-2 and Its Relationship to the Histidine Permease System

A histidine-binding protein has been isolated from the shock fluid of osmotically shocked Salmonella typhimurium and has been purified by conventional techniques. It has a molecular weight of 25,000 and binds 1 histidine molecule per molecule of protein. The binding protein is stable to wide variations of temperature, ionic strength, and pH. It binds histidine with a Kd of 1.5 µm. The protein also binds arginine but with a much weaker affinity. The transport of histidine by Salmonella typhimurium was found to be an energy-dependent process. The Km for histidine was 0.07 µm when measured by the growing cells method but it was 1 µm when determined in the presence of an inhibitor of protein synthesis. Histidine transport is inhibited by large excesses of arginine. Osmotically shocked exhibit a reduction in the initial rate and the steady state level of histidine accumulation. The simultaneous release of the histidine-binding protein and the reduction of transport caused by osmotic shock, as well as the similarity of kinetic constants and specificity of the binding protein and the histidine permease system suggest that the histidine-binding protein is a functional component of the histidine permease system.