Separation of two L-glutamine-hydroxylamine glutamyltransferases from rat liver.

The purification of glutamine synthetase (GS) from rat liver demonstrates that a small portion of glutamine-hydroxylamine-glutamyltransferase activity (GT) remains associated with GS activity (GT(S)). As GS is purified from the water extract, the ratio between GT(S) activity (GT(T)) is left to be extracted by KC1 from the pellet and, on further purification, appears to be independent of GS activity. Subtle differences in pH optimum, substrate requirement and reaction rates on addition of cofactors and amino acids in vitro and in responses to hormonal stimuli in vivo indicate that the glutamine transfer reaction may be catalyzed by two distinguishable proteins; only the minor component may be identical to GS.