Alteration of the Fe protein of nitrogenase by oxygen in the cyanobacterium Anabaena sp. strain CA.

Changes in protein composition were noted when heterocysts of Anabaena sp. strain CA were isolated from filaments grown in 1% CO2-99% N2 and subsequently exposed to oxygen. Immunospecific Western blot analysis showed that the Fe protein of nitrogenase is altered. In cells grown under microaerobic conditions, the Fe protein was found in a form with an apparent molecular weight of 30,000. Exposure to oxygen caused a shift in the migration of this polypeptide to a position corresponding to an apparent molecular weight of 31,500. This modification was reversible upon removal of oxygen from the culture. Chloramphenicol did not inhibit the alteration in either direction. Suppression by ammonium nitrate of the recovery of nitrogenase activity from the effects of oxygen did not prevent the alteration of the protein. Other inhibitors of nitrogenase activity, (metronidazole, carbonyl cyanide m-chlorophenylhydrazone, and phenazine methosulfate) were tested for their effect on Fe protein modification. Alteration of the Fe protein may relate to the protection of nitrogenase from the deleterious effects of oxygen.