Glutamate-binding protein and its relation to glutamate transport in escherichia coli K-12

Abstract

A highly specific, energy-dependent active transport system of glutamate has been found in Escherichia coli K-12. Mutants capable of utilizing glutamate as the sole carbon and energy source exhibit several-fold higher rates of glutamate uptake than the wild-type parent. Spheroplasts prepared from one such mutant, SC7, retain only 10–30% of the glutamate uptake capacity of intact cells. The capacity of spheroplasts for glutamate uptake can be fully restored by the addition of concentrated supernatant fluid obtained in the preparation of spheroplasts. This supernatant contains a protein fraction capable of binding L-glutamate with a K m of 6.7 × 10 −6M. L-glutamate-γ-methyl ester, a competitive inhibitor of glutamate uptake also inhibits competitively the binding of glutamate to the protein. L-alanine, a non-competitive inhibitor of glutamate uptake, inhibits its binding by the protein in a non-competitive fashion.