Precursor/product antiport in bacteria.

Many microorganisms metabolize their substrates (precursors) only partially and excrete the products of the metabolism into the medium. Although uptake of precursor and exit of product can proceed as two independent steps, there is increasing evidence that these processes are often linked and that transport is facilitated by a single antiport mechanism. Features of antiport mechanisms and advantages for the organism of catalysing precursor/product antiport will be illustrated by discussing a number of well-characterized systems. Based on precursor-product conversion stoichiometries, structural relatedness between precursors and products, and energetic and kinetic considerations, new examples of antiport systems will be proposed.