Rescue by vitamin B12 of Escherichia coli cells treated with colicins A and E allows measurement of the kinetics of colicin binding on BtuB

Abstract Sensitivity of Escherichia coli bacteria to colicins A and E1 was significantly increased by overproduction of the BtuB receptor protein. The amount of vitamin B₁₂ needed before colicins A and E1 treatment to protect cells against killing was found to be a function of the number of BtuB molecules present at the cell surface. Cells treated by colicins A and E were rescued from killing by addition of vitamin B₁₂ shortly after colicin treatment. The rate of reversal by vitamin B₁₂ may correspond to the kinetics of irreversible binding to BtuB of the various colicins.