《生物化学—代谢篇》第三十二章 生物固氮

第32章 生物固氮

第32章 生物固氮

自然界中的氮循环( The Nitrogen Cycle) by some anaerobic bacteria Amino acids nd other reduced synthesis in nitrogen-carbon plante and microorganisms degradation by animals and Ammonia anIsms Nitrate NO NHA nitrogen fixation by some bacterin (e. g, Klebsiella, Azotobacter Rhizobium) nitrification nitrifcation by soil bacteria by sod bacteria Nitrite Figure 21-1 NO2 of nitrogen fix 10 kg The total amount of nitrogen fixed annually in the biosphere exceeds 10kg

自然界中的氮循环（The Nitrogen Cycle ） The total amount of nitrogen fixed annually in the biosphere exceeds 1011 kg

固氮生物 共生型固 豆科植物的根瘤菌 氮微生物 非豆科植物(木麻黄属) 固氮 的根瘤菌 微生物 厌氧的巴氏梭菌,需氧固氮菌, 自生型固 厌氧和光合自养的蓝藻,需氧 氮微生物 和光合自养的细菌

固氮生物 固氮 微生物 共生型固 氮微生物 自生型固 氮微生物 豆科植物的根瘤菌 非豆科植物(木麻黄属) 的根瘤菌 厌氧的巴氏梭菌, 需氧固氮菌, 厌氧和光合自养的蓝藻,需氧 和光合自养的细菌

Cyanobacteria and rhizobia can fix n2 into armonia R leguminous ian

Cyanobacteria and Rhizobia can fix N2 into ammonia Rhizobia exist in nodules of leguminous plants

固氮反应 The reduction of n2 to NH3 is thermodynamically favorable no+3Ho-2NH 4G 0=-335kJ/mol But kinetically unfavorable: the bond energy for the triple bond in n2 is 942 kJ/mol oN+8H+ +8e +16ATP+16H,-> 2NH3+H2+16ADP+16P;

固氮反应 •N2 + 8H+ +8e - + 16ATP + 16H2O → • 2NH3 + H2 + 16ADP + 16Pi 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

固氮酶的结构 ■固氮酶复合物包括固氮酶和固氮酶还原酶。 固氮酶( dinitrogenase 两种肽链组成的四聚体:a2B2,活性中心在链 含有多个4Fe4 S centers和两个Mo- Fe clusters 称铁钼蛋白。 固氮酶还原酶( dinitrogenase reductase):由 两个相同的亚基组成,每个亚基含有一个Fe4-S4 redox center。又称铁蛋白 a The nitrogenase complex is highly conserved among different diazotrophs

固氮酶的结构 ◼ 固氮酶复合物包括固氮酶和固氮酶还原酶。 ◼ 固氮酶（ dinitrogenase ）： 两种肽链组成的四聚体：α2β2，活性中心在α链， 含有多个4Fe-4S centers 和两个 Mo-Fe clusters. 称铁钼蛋白。 ■固氮酶还原酶（ dinitrogenase reductase ）：由 两个相同的亚基组成，每个亚基含有一个Fe4 -S4 redox center。又称铁蛋白。 ◼ The nitrogenase complex is highly conserved among different diazotrophs

The nitrogenase complex consists of dinitrogenase and dinitrogenase redutase dinitrogenase(tetra dinitrogenase wpr FeMo protein dinitrogenase reductase(dimer) reductase(dimer or Fe pro t Fe-Mo cofactor 4Fe-4S ADP ADP 4Fe-4s 4Fe-4S (P-cluster) 4Fe-4S (P-cluster) ADP ADP (b) Fe-Mo cofactor

The nitrogenase complex consists of dinitrogenase and dinitrogenase redutase dinitrogenase (tetramer) or FeMo protein dinitrogenase reductase (dimer) or Fe protein dinitrogenase reductase (dimer) or Fe protein e - 4Fe-4S 4Fe-4S (P-cluster) Fe-Mo cofactor 4Fe-4S (P-cluster) 4Fe-4S ADP ADP ? Fe-Mo cofactor ADP ADP

N2 is believed to be reduced at the Fe-Mo cofactor Fe Fe Fe Fe Mor Molybdenum/N COO CH2 N/e e CHo HO→C—C00 CH2 cOo (c) Homocitrate

Molybdenum N2 is believed to be reduced at the Fe-Mo cofactor Fe Fe Fe Fe Fe Fe Fe S S S S S S S S S Mo

还原一分子N2需要8个电子 在固氮酶复合物上,消耗8个电子,将一分 子N2还原为2分子NH3,同时2个H被还原 为H2 电子来自于铁硫氧还蛋白( reduced ferredoxin, from photophosphorylation) x 黄素蛋白( reduced flavodoxin,from oxidative phosphorylation) 每传递一个电子需消化2个ATP,所释放的 能量用于改变固氮酶还原酶的构象,促进 电子的传递。 固氮酶的作用机制还不清楚,如固氮的同 时产生氢气的问题?

还原一分子N2需要8个电子 ◼ 在固氮酶复合物上，消耗8个电子，将一分 子N2还原为2分子NH3，同时2个H+被还原 为H2 . ◼ 电子来自于铁硫氧还蛋白(reduced ferredoxin， from photophosphorylation) 或 黄素蛋白 (reduced flavodoxin， from oxidative phosphorylation)。 ◼ 每传递一个电子需消化2个ATP，所释放的 能量用于改变固氮酶还原酶的构象，促进 电子的传递。 ◼ 固氮酶的作用机制还不清楚，如固氮的同 时产生氢气的问题？

coa+ 4CO9+ 4 pyruvate 4 acetyl-CoA Electrons are transferred to na bound in the 8 Ferredoxin or 8 Ferredoxin or 8 flavodoxin 8 flavodoxin active site of dinitrogenase (oxidized) (reduced) 8 via ferredoxin/ flavodoxin and dinitrogenase reductase 8 Dinitrogenase 8 Dinitrogenase reductase reductase (reduced) (oxidized) 16 ATP 16ADP +16P 8 Dinitrogenase 8 Dinitrogenase reductase (reduced reductase (oxidized +16ATP +16ATP 8 2H++2 2H++2e H+2 HH Dinitrogenase Dinitrogenase (oxidized) (reduced) N≡N→H-N=N-H→N一N 2NH3 HH 2NH H2 2H Diimine azine 4

Electrons are transferred to N2 bound in the active site of dinitrogenase via ferredoxin/flavodoxin and dinitrogenase reductase