Isolation and characterization of glutamine synthetase from the diazotroph Azospirillum brasilense

Abstract

1. 1. Glutamine synthetase was purified from the diazotroph Azospirillum brasilense. 2. 2. The holoenzyme with a M r of 630,000 is composed of 12 subunits of M r 52,000. 3. 3. A modified subunit of M r 53,000 was also found by electrophoresis under denaturing conditions. 4. 4. It is shown that the M r 53,000 species is the adenylylated subunit. 5. 5. The apparent K m values for glutamate, ATP and ammonia were 2.5 ± 0.3 mM, 200 ± 20 μM and42 ± 2 μM, respectively. 6. 6. Levels of glutamine synthetase activity in A. brasilense cells varied by a factor of 8 depending on the nitrogen source and its concentration in the growth medium.