3.2 Biological nitrogen fixation o 3.2. 1 Nitrogen fixation reduces nitrogen gas to ammonia, at the cost of ATP and reducing equivalent o N+16 atP+8e+8H-2NH+H+16 ADP +16 Pi o Eukaryotes cannot utilize dinitrogen, but some prokaryotes are able to catalyze the enzymatic reduction of this compound to ammonia o 3.2.2 Nitrogen fixation is sensitive to oxygen
3.2 Biological nitrogen fixation ⚫ 3.2.1 Nitrogen fixation reduces nitrogen gas to ammonia, at the cost of ATP and reducing equivalent. ⚫ N2 + 16 ATP + 8 e - + 8 H→ 2 NH3 + H2 + 16 ADP + 16 Pi ⚫ Eukaryotes cannot utilize dinitrogen, but some prokaryotes are able to catalyze the enzymatic reduction of this compound to ammonia. ⚫ 3.2.2 Nitrogen fixation is sensitive to oxygen
3.2.3 Enzymology of nitrogen fixation (A) (B) Nitrogenase complex Fe protein MoFe protein (NifH) (NifD, NifK FeMoco) Dinitrogenase Dinitrogenase Fe protein reductase MoFe 8 Fdx Sox 2 NH3+ H2 8 Faxed N2+8H Fe MoFered MoF Protein 16 ( ADP
3.2.3 Enzymology of nitrogen fixation
Table 3.2 Substrates and products of nitrogenase Substrate Product NH3 H+ H ●N,O N. HO NH3, CH4 CHCH
Table 3.2 Substrates and products of nitrogenase ⚫ Substrate Product ⚫ N2 NH3 ⚫ H+ H2 ⚫ N2O N2 , H2O ⚫ CN- NH3 , CH4 ⚫ C2H2 C2H4 , C2H6
3.3 Symbiotic nitrogen fixation
3.3 Symbiotic nitrogen fixation
3.3.1 Some vascular plants establish nitrogen-fixing symbioses o There are three major types of nitrogen-fixing symbioses o 1)Gram-negative bacteria, the rhizobia, form associations with numerous legume host plants(Fabaceae) and at least one non legume, Parasponia(ulmaceae) o 2)Gram-positive actinomycete genus( Frankia)and a diverse group a dicots, generally trees or woody shrubs from about 60 genera in 9 families, including alder(Alnus), myrtle( Myrica), Casuarina and Ceanothus o 3) Symbioses exist between cyanobacteria and a diverse array of plants: dicots(e.g, Gunnera), cycads, ferns,liverworts, and hornworts. Azolla, a water fern, associates symbiotically with the cyanobacterium
3.3.1 Some vascular plants establish nitrogen-fixing symbioses ⚫ There are three major types of nitrogen-fixing symbioses. ⚫ 1) Gram-negative bacteria, the rhizobia, form associations with numerous legume host plants (Fabaceae) and at least one non legume, Parasponia(Ulmaceae). ⚫ 2) Gram-positive actinomycete genus ( Frankia) and a diverse group a dicots, generally trees or woody shrubs from about 60 genera in 9 families, including alder(Alnus), myrtle(Myrica), Casuarina, and Ceanothus. ⚫ 3) Symbioses exist between cyanobacteria and a diverse array of plants: dicots (e.g.,Gunnera), cycads, ferns,liverworts, and hornworts. Azolla, a water fern , associates symbiotically with the cyanobacterium