Enzymology of biological nitrogen fixation. Final report, May 1, 1987--April 30, 1996

摘要

Fixation of nitrogen is accomplished by a variety of microorganisms, all of them procaryotic. Some operate independently and some function symbiotically or associatively with photosynthesizing plants. Biological nitrogen fixation is accomplished via the reaction: N2 + 8 H(+) + 8e(sup -) yields 2 NH3 + H2. This reaction requires a minimum of 16 ATP under ideal laboratory conditions, so it is obvious that the energy demand of the reaction is very high. When certain nitrogen-fixing organisms are supplied fixed nitrogen (e.g., ammonium) the organisms use the fixed nitrogen and turn off their nitrogenase system, thus conserving energy. When the fixed nitrogen is exhausted, the organism reactivates its nitrogenase. The system is turned off by dinitrogenase reductase ADP-ribosyl transferase (DRAT) and turned back on by dinitrogenase reductase-activating glycohydrolase (DRAG). The authors have investigated the details of how DRAT and DRAG are formed, how they function, and the genetics of their formation and operation.