Use of the sodium borohydride reduction technique to identify a gamma-glutamyl phosphate intermediary in the Escherichia coli glutamine synthetase reaction.

Incubation of unadenylylated Escherichia coli glutamine synthetase with ATP, L-[14C]glutamate and metal ion results in the formation of gamma-glutamyl-P which can under appropriate conditions be reduced by sodium borohydride. The acyl-P compound is formed catalytically as judged by the quantity of radioactive alpha-amino-delta-hydroxyvalerate produced compared to the concentration of enzyme subunits. Formation of the glutamyl-P compound occurs in the presence of magnesium or manganous ions, and the relation of this apparent lack of metal ion specificity with regard to the highly specific Mg2+-supported biosynthetic activity of the unadenylylated form is discussed.