Occurrence of Isóenzymes of Glutamine Synthetase in the Alga Chlorella kessleri

Abstract

Two forms (GS(1) and GS(2)) of glutamine synthetase have been isolated, separated by ion exchange chromatography, and partly characterized from cells of the green alga Chlorella kessleri. Both forms are present in cells grown autotrophically or heterotrophically on various nitrogen sources, but under all nutritional conditions GS(1) was found to be the major isoenzyme present (60-80%). The activity of both isoenzymes was greatest in cells grown under nitrogen-limiting conditions. Both isoenzymes have molecular weights in the range 340 to 350,000 daltons. GS(1) was found to have a greater thermostability than GS(2): GS(1) was stable at 30 degrees C while GS(2) lost 95% of its activity in 30 minutes. GS(1) was much less sensitive to thiol reactive reagents than GS(2).