Regulation of nitrogenase activity by covalent modification in Chromatium vinosum

Nitrogenase in Chromatium vinosum was rapidly, but reversibly inhibited by NH ₄ ⁺ . Activity of the Fe protin component of nitrogenase required both Mn²⁺ and activating enzyme. Activating enzyme from Rhodospirillum rubrum could replace Chromatium chromatophores in activating the Chromatium Fe protein, and conversely, a protein fraction prepared from Chromatium chromatophores was effective in activating R. rubrum Fe protein. Inactive Chromatium Fe protein contained a peptide covalently modified by a phosphate-containing molecule, which migrated the same in SDS-polyacrylamide gels as the modified subunit of R. rubrum Fe protein. In sum, these observations suggest that Chromatium nitrogenase activity is regulated by a covalent modification of the Fe protein in a manner similar to that of R. rubrum.Abbreviation HEPES N-2-hydroxyethyl piperazine-N-2-ethanesulfonic acid