title: Presence of a second mechanism for the posttranslational regulation of nitrogenase activity in Azospirillum brasilense in response to ammonium.
abstract: Although ADP-ribosylation of dinitrogenase reductase plays a significant role in the regulation of nitrogenase activity in Azospirillum brasilense, it is not the only mechanism of that regulation. The replacement of an arginine residue at position 101 in the dinitrogenase reductase eliminated this ADP-ribosylation and revealed another regulatory system. While the constructed mutants had a low nitrogenase activity, NH4+ still partially inhibited their nitrogenase activity, independent of the dinitrogenase reductase ADP-ribosyltransferase/dinitrogenase reductase activating glycohydrolase (DRAT/DRAG) system. These mutated dinitrogenase reductases also were expressed in a Rhodospirillum rubrum strain that lacked its endogenous dinitrogenase reductase, and they supported high nitrogenase activity. These strains neither lost nitrogenase activity nor modified dinitrogenase reductase in response to darkness and NH4+, suggesting that the ADP-ribosylation of dinitrogenase reductase is probably the only mechanism for posttranslational regulation of nitrogenase activity in R. rubrum under these conditions.
authors.affiliation: Department of Biochemistry, University of Wisconsin-Madison 53706, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Zhang
authors.forename: R H
authors.initials: RH
authors.lastname: Burris
authors.forename: P W
authors.initials: PW
authors.lastname: Ludden
authors.forename: G P
authors.initials: GP
authors.lastname: Roberts
mesh_terms: D036002:ADP Ribose Transferases; D015806:Azospirillum brasilense / Q000187:drug effects / Q000201:enzymology / Q000235:genetics*; D017037:Dinitrogenase Reductase / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D005798:Genes, Bacterial; D006026:Glycoside Hydrolases; D016297:Mutagenesis, Site-Directed; D009699:N-Glycosyl Hydrolases; D009586:Nitrogen Fixation / Q000235:genetics; D009591:Nitrogenase / Q000096:biosynthesis*; D011499:Protein Processing, Post-Translational; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D012247:Rhodospirillum rubrum / Q000201:enzymology / Q000235:genetics; D013045:Species Specificity
chemical_list: D017037:Dinitrogenase Reductase; D000644:Quaternary Ammonium Compounds; D009591:Nitrogenase; D036002:ADP Ribose Transferases; C057637:dinitrogenase reductase ADP-ribosyltransferase; D006026:Glycoside Hydrolases; D009699:N-Glycosyl Hydrolases; C036091:ADP-ribosyl-(dinitrogen reductase) hydrolase