Chapter 22 Biosynthesis of amino acids nucleotides and related molecules Reduction (fixation) of N into ammonia (NH3 or NH 2.Synthesis of the 20 amino acids. 3. Synthesis of other biomolecules from amino acids 4. The de novo pathways for purine and pyrimidine biosynthesis 5. The salvage pathways for purine and pyrimidine reuse
Chapter 22 Biosynthesis of amino acids, nucleotides and related molecules 1. Reduction (fixation) of N2 into ammonia (NH3 or NH4 + ) 2. Synthesis of the 20 amino acids. 3. Synthesis of other biomolecules from amino acids 4. The de novo pathways for purine and pyrimidine biosynthesis. 5. The salvage pathways for purine and pyrimidine reuse
1, The nitrogenase complex in certain bacteria(( diazotrophs,;圆氮生勒 catalyzes the conversion of N, to NH Cyanobacteria (photosynthetic) and rhizobia (symbiont) can fix N, into NH3 The reduction of n to nh, is thermodynamically favorable 3H 2NH2 4G0=-33. 5kJ/mol for the tuple bond in N, is 942 \mo ergy But kinetically unfavorable: the bond e
1. The nitrogenase complex in certain bacteria (diazotrophs,固氮生物) catalyzes the conversion of N2 to NH3 • Cyanobacteria (photosynthetic) and rhizobia (symbiont) can fix N2 into NH3 . • The reduction of N2 to NH3 is thermodynamically favorable : • N2 + 3H2 2NH3 G` o=-33.5kJ/mol • But kinetically unfavorable: the bond energy for the triple bond in N2 is 942 kJ/mol
The nitrogenase(固氮酶) complex mainly consists of two types of enzymes: the dinitrogenase and the dinitrogenase reductase The dinitrogenase(containing molybdenum thus called the MoFe protein) is a tetramer of two different subunits, containing multiple 4Fe-4S centers and two Mo-Fe clusters The dinitrogenase reductase(also called the Fe protein) is a dimer of two identical subunits, containing a single FeaS, redox center. The nitrogenase complex is highly conserved among different diazotrophs
• The nitrogenase (固氮酶) complex mainly consists of two types of enzymes: the dinitrogenase and the dinitrogenase reductase. • The dinitrogenase (containing molybdenum, thus called the MoFe protein) is a tetramer of two different subunits, containing multiple 4Fe-4S centers and two Mo-Fe clusters. • The dinitrogenase reductase (also called the Fe protein) is a dimer of two identifcal subunits, containing a single Fe4 -S4 redox center. • The nitrogenase complex is highly conserved among different diazotrophs
Cyanobacteria and Rhizobia can fix N2 into ammonia R n leg an
Cyanobacteria and Rhizobia can fix N2 into ammonia Rhizobia exist in nodules of leguminous plants
The nitrogenase complex The dinitrogenase reductase(dimer The dinitrogenase reducto dimer) st oike dinitrogenase (tetramer) Fe-Mo cofactor ADP 4Fe-4s CHa CHa 4Fe-4S HO-C-COO 4Fe-4S ADP COO (P-cluster) Homocitrate
The nitrogenase complex The dinitrogenase (tetramer) The dinitrogenase reductase (dimer) The dinitrogenase reductase (dimer) ADP ADP 4Fe-4S 4Fe-4S 4Fe-4S (P-cluster) Fe-Mo cofactor
2. Electrons are transferred through a series- of carriers to 2 r its reduction on the nitrogenase complex Eight electrons are believed to be needed for each round of fixation reaction: with six for reducing one n2 and two for reducing 2 H** (to form H2) The electrons mainly come from reduced ferredoxin(from photophosphorylation) or reduced flavodoxin(from oxidative ph hosphorylation) and are transferred to dinitrogenase via dinitrogenase reductase
2. Electrons are transferred through a series of carriers to N2 for its reduction on the nitrogenase complex • Eight electrons are believed to be needed for each round of fixation reaction: with six for reducing one N2 and two for reducing 2 H+ (to form H2 ). • The electrons mainly come from reduced ferredoxin (from photophosphorylation) or reduced flavodoxin (from oxidative phosphorylation) and are transferred to dinitrogenase via dinitrogenase reductase
For each electron to be transferred from dinitrogenase reductase to dinitrogenase, two ATPs are hydrolyzed causing a conformational change which reduces the electron affinity for the reductase (i.e, an increased reducing power) The oxidized and reduced dinitrogenase reductase dissociates from and associates with the dinitrogenase, respectively The overall reaction catalyzed is N,+8H++8+16ATP+16H,O 2NH +H+16ADP+16P
• For each electron to be transferred from dinitrogenase reductase to dinitrogenase, two ATPs are hydrolyzed causing a conformational change which reduces the electron affinity for the reductase (i.e., an increased reducing power). • The oxidized and reduced dinitrogenase reductase dissociates from and associates with the dinitrogenase, respectively. • The overall reaction catalyzed is: • N2 + 8H+ +8e - + 16ATP + 16H2O → • 2NH3 + H2 + 16ADP + 16Pi
cOa+ 4CO2+ 4 pyruvate 4 acetyl-CoA Electrons are transferred to N bound in the 8 Ferredoxin or 8 flavodoxin 6 B naydasinor) active site of dinitrogenase (oxidized) (red via ferredoxin/flavodoxin land dinitrogenase reductase Dinitrogen 8 Dinitrogenase reductase reductase (reduced) (oxidized) 16 ATP 个 16ADP +16P; 8 Dinitrogenase 8 Dinitrogenase reductase(reduced reductase(oxidized) +16ATP + 16ATP Dinitrogenase Dinitrogenase 2H++2e 2H+2e 2H+2e (oxidized) H N≡N H-N=N一H 2N H 2NH扌H2 N Diimine Hydrazine
Electrons are transferred to N2 bound in the active site of dinitrogenase via ferredoxin/flavodoxin and dinitrogenase reductase
Mo is believed to bind to the cavity of the Fe-Mo cofactor of the dinitrogenase active site. F 于e Fe e
N2 is believed to bind to the cavity of the Fe-Mo cofactor of the dinitrogenase active site
