The Urea Cycle Begins with the Formation of Carbamoyl Phosphate The urea cycle begins with the coupling of free NH4 with HCO3- to form carbamoyl phosphate.The synthesis of carbamoyl phosphate,though a simple molecule,is complex,comprising three steps,all catalyzed by carbamoyl phosphate synthetase. ATP ADP HO HO HO NH NH Bicarbonate Carboxyphosphate Carbamic acid Carbamoyl phosphate
The Urea Cycle Begins with the Formation of Carbamoyl Phosphate • The urea cycle begins with the coupling of free NH4 + with HCO3 - to form carbamoyl phosphate. The synthesis of carbamoyl phosphate, though a simple molecule, is complex, comprising three steps, all catalyzed by carbamoyl phosphate synthetase
The reaction begins with the phosphorylation of HCO3 to form carboxyphosphate,which then reacts with ammonium ion to form carbamic acid.Finally,a second molecule of ATP phosphorylates carbamic acid to carbamoyl phosphate.The structure and mechanism of the fascinating enzyme that catalyzes these reactions will be discussed in Chapter 25.The consumption of two molecules of ATP makes this synthesis of carbamoyl phosphate essentially irreversible.The mammalian enzyme requires N-acetyl-glutamate for activity,as will be discussed shortly
• The reaction begins with the phosphorylation of HCO3 - to form carboxyphosphate, which then reacts with ammonium ion to form carbamic acid. Finally, a second molecule of ATP phosphorylates carbamic acid to carbamoyl phosphate. The structure and mechanism of the fascinating enzyme that catalyzes these reactions will be discussed in Chapter 25.The consumption of two molecules of ATP makes this synthesis of carbamoyl phosphate essentially irreversible. The mammalian enzyme requires N-acetyl-glutamate for activity, as will be discussed shortly
鸟氨酸（脲）循环概况 ·2分子氨和1分子二氧化碳+1分子尿素 （1分子氨是游离的，1分子氨来自天冬氨酸) ·合成一分子尿素消耗4分子ATP ·反应部位；肝脏（线粒体+细胞质） ·人类发现的第一个环式代谢途径 Krebs&Henseleit1932年提出 CO2 NH 3 ATP aspartate 2 H2O urea 2 ADP 2 P;+AMP PP;fumarate
鸟氨酸(脲)循环概况 • 2分子氨和1分子二氧化碳→1分子尿素 （1分子氨是游离的，1分子氨来自天冬氨酸） • 合成一分子尿素消耗4分子ATP • 反应部位；肝脏（线粒体+细胞质） • 人类发现的第一个环式代谢途径 • Krebs&Henseleit 1932年提出
The Urea Cycle. H2O Fumarate Arginine H>N NH- Urea Argininosuccinate Ornithine Carbamoyl Aspartate Citrulline phosphate R—NH2 R NH2 CYTOSOL MITOCHONDRIAL MATRIX CO2 NH4*
The Urea Cycle
0-C-0H Bicarbonate ATP ADP OH Carbonic-phosphoric acid anhydride NH P H2N-C- OH Carbamate ATP ADP H2N- Carbamoyl phosphate 氨甲酰磷酸生成时消耗2分子高能磷酸键
氨甲酰磷酸生成时消耗2分子高能磷酸键