FIG. 1.

Nitrogenase switch-off and ADP-ribosylation of NifH in glnB and glnK mutants. R. capsulatus cells were grown under N₂-fixing conditions. Gas samples were withdrawn at the indicated times and assayed for in vivo nitrogenase activity by the acetylene reduction method. Acetylene was added at time 0. For panels A to D, NH₄Cl was added to 200 μM at 25 min. (A) Wild-type (B10S). (B) glnB (PHU332). (C) glnK (BSRUB13). (D) glnK51 (GlnK-Y51F; BSRUB13/pAP2). For panels E and F, NH₄Cl was added to 50 mM at 25 min. (E) glnB (PHU332). (F) glnK (BSRUB13). The ADP ribosylation state of NifH was monitored for the wild type (B10S) and glnB (PHU332), glnK (BSRUB13), and glnK51 (GlnK-Y51F; BSRUB13/pAP2) mutants (G). Where indicated, NH₄Cl was added to 50 mM at 25 min.