Comparison of several forms of glutamine synthetase from Escherichia coli

Abstract

The preparation of three forms of glutamine synthetase from Escherichia coli is described: 1. active glutamine synthetase (GSa) from derepressed cells, grown on an ammonia free medium, 2. glutamine synthetase inactivated in vivo [GSb(vv)] by addition of ammonium salts to the culture medium, 3. glutamine synthetase inactivated in vitro [GSb(vt)] by the “inactivating enzyme” in the presence of ATP, Mg2+, and glutamine. GSa has a high activity in the glutamine synthetase reaction as well as in the glutamyl transferase reaction, whereas GSb(vv) and GSb(vt) have low activities in the glutamine synthetase reaction and high activities in the glutamyl transferase reaction. GSb(vv) and GSb(vt) behave similarly in catalytic properties and in feedback inhibition. There are no differences between the two preparations of GSb in the sedimentation in the ultracentrifuge, in electrophoresis on agar gel or polyacrylamide and in chromatography on DEAE cellulose. These results indicate, that GSb(vv) and GSb(vt) are identical. This leads to the conclusion, that the in vitro inactivation and the in vivo inactivation are caused by the same reaction. The sedimentation constants as well as the optical rotatory dispersion of GSa and of the two forms of GSb are identical. No separation of the three modifications of GS were achieved by chromatography on DEAE‐cellulose or by electrophoresis. The effects of allosteric effectors in the synthetase reaction are the same although GSb has in this reaction only 5–10% of the activity of GSa. As compared to GSa the two GSb preparations exhibit in the UV spectrum a shift of the absorption maximum to shorter wavelenghts.