ISOLATION AND CHARACTERIZATION OF 2 FORMS OF GLUTAMINE-SYNTHETASE FROM SOYBEAN HYPOCOTYL

Two forms of glutamine synthetase have been isolated from four-day-old, etiolated soybean hypocotyls by a procedure involving protamine sulfate and ammonium sulfate precipitation, and DEAE-cellulose and Bio-Gel chromatography. The two activities, which eluted from DEAE-cellulose at 0.1 M and 0.8 M KCl, were further purified on Bio-Gel columns to a total purification of 500- and 2000-fold, respectively. The enzymes were characterized by similar molecular weights of 365,000, similar pH and temperature optima, and a similar apparent Km for hydroxylamine. The enzymes differed with respect to their apparent Km for glutamine and their degree of association with ADP. Preincubation in the presence of ADP resulted in a stabilization to thermal denaturation. © 1979.