Effect of Solute Size on Diffusion Rates through the Transmembrane Pores of the Outer Membrane of Escherichia coli

I N T R O D U C T I O N Cells o f Gram-nega t ive bacter ia , for example , Escherichia coli and Salmonella typhimurium, are enclosed by a double layer o f uni t m e m b r a n e (Glauer t and Thorn ley , 1969). T h e inner m e m b r a n e corresponds to the cytoplasmic membrane. T h e ou te r m e m b r a n e is located outs ide the rigid pep t idog lycan layer and corresponds to the ou te rmos t layer o f the "cell wal l" (Nikaido and Nakae, 1979). We have shown tha t the ou te r m e m b r a n e o f E. coli and S. typhimurium is pe rmeab le to monosacchar ides , disaccharides, and t r isaccharides by measuring the equi l ib r ium dis t r ibut ion o f labeled saccharides be tween the external m e d i u m and the "per ip lasmic space," i.e., the space be tween the ou te r and inner membranes (Decad and Nikaido, 1976). T h e c o m p o n e n t responsible for this pe rmeab i l i ty was ident if ied as a special class o f prote in , porins, by the following approaches . (a) Porins were purif ied from the ou te r membranes , J. GEN. PHYSIOL. 9 The Rockefeller University Press 9 0022-1295/81/02/0121/15 $1.00 121 Volume 77 February 1981 121-135 on F ebuary 1, 2013 jgp.rress.org D ow nladed fom Published February 1, 1981