Indole inhibition of cofactor activated bacteriophage

Abstract

Certain bacteriophage strains must be activated by a cofactor before attachment to their host cells is possible. In some of these strains indole competitively inhibits the activation. This inhibition by indole is the subject of the present study. The following sets of measurements were made: 1) Kinetics of the approach to equilibrium from both sides. 2) Deactivation in the presence of indole. 3) Activation in cofactor after pre-equilibration with indole. 4) Measurements of the equilibrium activity in the presence of various cofactor-indole mixtures. The following principal conclusions may be drawn: 1) A true thermodynamic equilibrium exists between indole-deactivated virus and active virus. 2) The presence of indole increases the rate of deactivation of the virus population in the absence of external cofactor, over that found when only cofactor is removed. 3) Indole combines only with active phage particles. 4) At equilibrium in the presence of high concentrations of cofactor and in the range of strong inhibition, the activity is inversely proportional to the concentration of indole. These findings make it necessary to modify the theory of activation previously developed by Stent and Wollman. It is assumed that the surface of the phage particle, during the process of activation, undergoes a structural change perhaps similar to the reversible denaturation of proteins.