Separation, Purification, and Characterization of two Isoforms of Glutamine Synthetase from Chlamydomonas Reinhardii

Abstract

Two isoforms of glutam ine synthetase, GS| and GS2, have been separated from Chlamydomonas reinhardii cells grown autotrophically with nitrate. The intracellular level of GS2 was higher than that of GS1,. In cells under darkness, the GS1, peak increased markedly, whereas that of GS2 becam enegligible. The two isoenzymes were purified to electrophoretic homogeneity by a method which included: a) DE-52 cellulose chromatography; b) ammonium sulphate fractionation; and c) affinity chromatography on ADP-sepharose. The specific activity was 114 and 63 U/mg for GS1, and GS2 respectively, and both enzymes (Mr = 380 000 and 373 000) are oligomeric proteins composed by 8 subunits of similar size (Mr = 48 000 in GS1), and 46 000 in GS2). The basic differences between GS, and GS2 are: a) the effect of light on their intracellular level; b) their for ammonium (83 and 244 μm, respectively). Both isoenzymes were inhibited in a similar extent by L-alanine, L-glycine and L-arginine. © 1983, Walter de Gruyter. All rights reserved.