Isolation and characterization of glutamine synthetase from the diazotroph Azospirillum brasilense |
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Affiliation: | Dipartimento di Fisiologia e Biochimica Generall, Universita'' di Milano, via Celoria 26, Milano 1-20133, Italy [Tel. +39270644505; Fax +3922361070] |
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Abstract: | - 1.1. Glutamine synthetase was purified from the diazotroph Azospirillum brasilense.
- 2.2. The holoenzyme with a Mr of 630,000 is composed of 12 subunits of Mr 52,000.
- 3.3. A modified subunit of Mr 53,000 was also found by electrophoresis under denaturing conditions.
- 4.4. It is shown that the Mr 53,000 species is the adenylylated subunit.
- 5.5. The apparent Km 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.
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