Influence of molecular size and osmolarity of sugars and dextrans on the synthesis of outer membrane proteins O-8 and O-9 of Escherichia coli K-12

Abstract

Supplementation of the growth medium with high concentrations of sugars or low-MW dextrans results in a drastic change in the ratio of outer membrane proteins O-8 and O-9, due to induction of O-8 synthesis and suppression of O-9 synthesis. Sugars and dextrans of MW greater than 600-700 switched the synthesis of O-9 to that of O-8 more effectively than those of lower MW, although the effect was almost the same within each of the 2 groups irrespective of the differences in MW within the group. Proteins O-8 or O-9, or both, are responsible for the formation of pores that allow the passive diffusion of hydrophilic molecules whose MW are smaller than about 600. Substances that cannot pass through the outer membrane apparently switch the synthesis of O-9 to that of O-8 more effectively than those that can penetrate this membrane with the aid of O-8, O-9 or both. The osmotic pressure exerted on the outer membrane probably plays an important role in the regulation of synthesis of the 2 proteins.