Cytochrome o as a terminal oxidase and receptor for aerotaxis in Salmonella typhimurium

Cytochrome o was the only oxidase of the electron transport system that was present in exponentially growing Salmonella typhimurium ST1. Identification of cytochrome o was made by the (CO-reduced)-minus-(reduced) difference spectra and by the photochemical action spectrum of the relief, by light, of CO-inhibited respiration. Cytochrome o also functioned as the receptor for chemotaxis to oxygen (aerotaxis). The concentration of oxygen that elicits the maximum response for aerotaxis (0.7 microM) was similar to the Km for respiration (0.74 microM), and both aerotaxis and respiration were blocked 5 mM KCN.