The adsorption of coliphage lambda to its host: Effect of variations in the surface density of receptor and in phage-receptor affinity

Abstract

When measured in the presence of optimal concentrations of cations (2 × 10 −3 mMg 2+ for instance), the rate of adsorption of phage lambda to cells of Escherichia coli K12 increases only about tenfold when the density of receptor protein at the cell surface increases from about 30 molecules per cell (glucose-grown cells) to 6000 molecules per cell (maltose-grown cells). At low densities of receptor, variations in the concentration of divalent cations affect the rate of phage adsorption in the same way as they affect phage-receptor affinity in vitro. In particular the rate of adsorption is very much decreased when the concentration of Mg 2+ ions is increased to 2 × 10 −2 m. This is not true, however, when the density of receptor is high, in which case an increase in the concentration of Mg 2+ ions to 2 × 10 −2 m only slightly decreases the rate of adsorption. An interpretation for these facts is proposed, which takes into account the geometrical and physical properties of the elements involved, as well as the known characteristics of phage-receptor interaction in vitro. This interpretation relates phage adsorption to the more general problem of membrane-ligand interaction.