Cell walls of E. coli strains B and Cullen contain specific receptors for colicin K and for the T2, T6, and C16 phages. The receptors for the bacteriocin and the T6 virus are located in the outer layers of the cell wall of these microorganisms and are absent in their cytoplasmic membrane.
The receptors for colicin K, phage T2, and the T6 and C16 viruses differ in their stability toward enzymes and chemical reagents. Their specificity must therefore be determined by different chemical groupings.
The colicin K receptor is inactivated by certain proteolytic enzymes and by reagents which combine with tryptophan. It is concluded therefore that proteins or peptides containing this amino acid are essential for biological activity of the receptor.