Characterization of Glutamine Synthetase Isoforms from Chlorella

Ion-exchange chromatography of extracts derived from Chlorella sorokiniana mutant strain (oxygen resistant) yielded two separate activity peaks of glutamine synthetase (GS). $\text{GS}_{\text{I}}$ and $\text{GS}_{\text{II}}$ were purified 220- and 187-fold and have molecular weights of approximately 398,000 and 360,000, respectively. Both enzymes are composed of eight identical subunits with a subunit molecular weight of 47,000 for $\text{GS}_{\text{I}}$ and 43,000 for $\text{GS}_{\text{II}}$. The amino acid composition, catalytic, and immunological properties for both enzymes are similar.