Differential release of periplasmic versus cytoplasmic enzymes from Escherichia coli B by polymyxin B

5 to 6% of the total cellular protein was released into the medium from Escherichia coli B which was harvested from a logarithmically growing culture in a glycerol-salts medium, suspended in 0.14 M NaCl, pH 7.3, at a tenfold cell density (about 1.5×10¹⁰/ml or 1.6 mg protein/ml) and treated for 1 min at 37° C with 200 μg polymyxin B/ml. The protein patterns of this material obtained by polyacrylamide gel electrophoresis were identical with those derived from an osmotic shock supernatant according to Neu and Heppel (1965). Periplasmic enzyme activities found in the polymyxin-supernatant included 5′-nucleotidase, 3′-nucleotidase, ribonuclease I, acid phosphatase and alkaline phosphatase. Upon further incubation with polymyxin B (up to 60 min), cell autolysis occurred with a concomitant release of 68% of total protein and up to 100% of cytoplasmic enzyme activities like β-galactosidase, inorganic pyrophosphatase and aldolase. This autolysis was not observed with stationary phase cells or with cells grown in a complex yeast extract-glucose broth. The mechanism of action of polymyxin B leading to the specific release of periplasmic proteins in discussed.