Separation of Two L-Glutamine-Hydroxylamine Glutamyltransferases from Rat Liver

Abstract

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) and GS remains constant. The major portion of the GT 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.

Amino Acid Metabolizing Enzymes in Rat Submaxillary Gland, Normal or Neoplastic, and in Pancreas

“…Glutamyl transferase activity [12] was essentially absent from pancreas. Both sub maxillary gland and pancreas had low alanine aminotransferase activities.…”

“…The varying ratios between glutamyl transferase and glutamine synthe tase activities (ranging from 45 in liver to 2.3 in pancreas), observed pre viously in other mammalian and avian tissues [9,13], suggest that pancreas, like rat muscle and heart, contains essentially only glutamine synthetase II with its associated low glutamyl transferase (GT(S)) activity [13] while sub maxillary gland, like rat liver and brain, contains both glutamine synthetase (with GT(S) activity) and glutamyl transferase [12].…”

Glutamine Synthetase and Glutamyltransferase in Developing Chick and Rat Tissues

“…Since GT has no known physiological acceptor or function and GS has been shown to catalyze the GT reaction to a variable extent (5,7,9,10), GT measure ments have been attributed to GS and have been identified with measurements of the competence of a tissue to form glutamine (9,20). It is clear that in chick tissues, as previously shown in rat liver, at least two separate enzymes are impli cated in the GS and GT reactions.…”