RECEPTOR INTERACTIONS IN A SIGNALING SYSTEM - COMPETITION BETWEEN RIBOSE RECEPTOR AND GALACTOSE RECEPTOR IN CHEMOTAXIS RESPONSE

Galactose and ribose receptors [Salmonella typhimurium] compete for a common site by comparing the specificities of the purified receptors with the specificity of the whole organism response. Ribose does not bind to the purified galactose receptor but inhibits the in vivo galactose response. A mutant lacking the ribose receptor shows no inhibition of the galactose response even at very high ribose concentrations. The results can be explained by a mechanism involving a ligand-induced conformational change in the receptor which produces a combining site with affinity for the molecule that serves as a 1st component of the signalling system and a limited number of such 1st component molecules that cannot bind both receptors simultaneously. The mechanism may have considerable generality for sensory, hormonal and transport systems.