Penicillin-binding proteins of Escherichia coli. Comparison of a strain carrying an R-factor and the parent strain.

Both from Escherichia coli K12 W3630 carrying an R-factor, R+75, and from the parent strain at least six penicillin- and cephalosporin-binding proteins were obtained as soluble forms. The molecular weights of the binding proteins of the strain carrying an R-factor were similar to those of the parent strain and not affected by the presence of an R-factor which specified the production of a beta-lactamase. Gel filtration with [14C]benzylpenicillin suggested the equimolar binding of benzylpenicillin to each binding protein. Three binding proteins of E. coli carrying R+75 and two binding proteins of the parent strain were purified by affinity chromatography followed by gel filtration. In fluorescence titration, various penicillins and cephalosporins were shown to bind to the purified binding proteins and their association constants were in the range of 0.4 to 21-10(3) M-1. The binding proteins of both strains did not react with the antibody against the beta-lactamase specified by R+75.