Lysine excretion by Corynebacterium glutamicum. 2. Energetics and mechanism of the transport system

Abstract

Lysine excretion in Corynebacterium glutamicum was characterized as secondary transport process. It is modulated by three forces: the membrane potential, the chemical potential of lysine, and the proton gradient. The ATP content of the cells did not correlate with the export activity. Lysine is excreted in symport with presumably two OH- ions which is not distinguishable experimentally from an antiport mechanism against two protons. The substrate-loaded carrier is uncharged. When the external substrate concentration is low and no proton gradient present, reorientation of the positively charged, unloaded carrier is rate-limiting. Export then depends on the membrane potential. When the external substrate is high, translocation of the loaded, uncharged carrier is rate-limiting, and export is not modulated by the membrane potential. The lysine secretion system in C. glutamicum is shown to be well adapted to the requirements of metabolite export.