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 6.20 sThe nitrogen in amino acids, purines, pyrimidines and other biomolecules ultimately comes from atmospheric nitrogen Cyanobacteria(蓝藻细菌 瘤菌, symbiont)cm/蔺 photosynthetic) and rhizobia(报 ix N, into nha The reduction of N, to NH, is thermodynamically favorable =N2+6e96H2NH31G0=-33.5kJ/mol But kinetically unfavorable: the bond energy for the triple bond in N, is 942 kJ/mol
1. The nitrogenase complex in certain bacteria (diazotrophs,固氮生物) catalyzes the conversion of N2 to NH3 • The nitrogen in amino acids, purines, pyrimidines and other biomolecules ultimately comes from atmospheric nitrogen. • Cyanobacteria (蓝藻细菌, photosynthetic) and rhizobia (根 瘤菌, symbiont) can fix N2 into NH3 . • The reduction of N2 to NH3 is thermodynamically favorable : • N2 + 6e- + 6H+ 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, tE 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 4 Fe-4S 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，钼, 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 4Fe-4S 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) e-3S Fe-Mo cofactor BFe-3S 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 3Fe-3S 3Fe-3S Mo
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 nitrogenase is in imperfect enzyme: H, is formed along with NH
• 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 nitrogenase is in imperfect enzyme: H2 is formed along with NH3
The overall reaction catalyzed is 8H+8e+16ATP+16H20→ 2NH2 + H,+16ADP+16P
• 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 3Fe-3s dinitrogenase active site. F 于e Fe 3Fe-3S e
N2 is believed to bind to the cavity of the Fe-Mo cofactor of the dinitrogenase active site. 3Fe-3S 3Fe-3S
