Cell surface proteins of E. coli

Cell surface proteins of $\text{E. coli}$ K12 have been labelled with ¹²⁵I using a lactoperoxidase method. Results suggest that most outer membrane proteins so far characterised appear to have at least part of their polypeptide chain on the cell surface. These include major outer membrane protains I and II¹, the maltose and vitamin B₁₂ binding proteins and proteins involved in iron transport. The labelling of an antibiotic sensitive mutant and its parent were compared but their labelling patterns did not appear to differ in any way which would suggest the cause of the permeability difference between these two strains.