Chapter 19 Uptake of solutes through bacterial outer membranes

Abstract

This chapter discusses the uptake of solutes through bacterial outer membranes. The cell envelope of Gram-negative bacteria consists of three different layers: the outer membrane, the murein, and the inner membrane. The inner membrane represents a real diffusion barrier and contains the respiration chain, a large number of transport systems, and the machinery for protein export. Murein is a large hetero-polymer that confers the rigidity of the cell envelope, the shape of the cell, and protects it from osmotic lysis. The outer membrane of Gram-negative bacteria plays an important role in the physiology of these organisms. Most porins form transmembrane channels that sort solutes mainly according to their molecular masses and have little solute specificity. These porins represent general diffusion channels. The primary structure of many porins has been resolved from the basis of their amino acid or their cDNA sequence. The sequences are not particularly hydrophobic, which means that the arrangement of the proteins in secondary and tertiary structure is responsible for their function as membrane channels.