Sodium‐dependent isoleucine transport in the methanogenic archaebacterium Methanococcus voltae

Methanococcus voltae possesses a Na + ‐dependent transport system for isoleucine which requires for optimum rates a CO 2 /H 2 atmosphere. The K m for the system is 4.5 μM with a V max of 1.5 nmol·min −1 ·mg dry wt −1 . Approximately 75% of the label can be released from the cell pool following short‐term experiments with gradients of isoleucine reaching 100 (in/out). Transport is inhibited by ionophores and N ‐ethyl maleimide. Only valine and leucine effectively compete with isoleucine for transport.