Characterization of colicin Ia and colicin Ib. Purification and some physical properties.

Colicins Ia and Ib have been purified from mitomycin C-induced Escherichia coli strains W3110 str-r (co1 Ia) and W3110 str-r (co1 Ib) by ammonium sulfate precipitation, treatment with diethylaminoethylcellulose, and chromatography on DEAE-Sephadex, phosphocellulose, and hydroxylapatite. Sedimentation velocity and equilibrium centrifugation as well as polyacrylamide gel electrophoresis at several pH values indicated that both colicin preparations were homogeneous. The molecular weight of colicin Ia was determined from its &I,~ (3.57 S) and D&+ (4.12 X 1OF cm2 set-r) as well as from sedimentation equilibrium centrifugation and dodecyl sulfate polyacrylamide gel electrophoresis to be approximately 77,600. The molecular weight of colicin Ib was approximately 79,600 (a!&, = 3.67 S; D&W = 4.32 x lo-’ cm2 set-l). Colicins Ia and Ib had f/j0 values of 1.82 and 1.76, respectively.