西北大学生物化学___蛋白质代谢.ppt

Cys is synthesized from homocysteine(which is derivedfrom Met) and Serin mammals (胱硫醚b-合成酶) (胱硫醚g-裂解酶) Homocysteine (高半胱氨酸） P354 P355 三、芳香族氨基酸及组氨酸的生物合成 （一）苯丙氨酸、酪氨酸及色氨酸的生物合成 1. 由分支酸形成苯丙氨酸和酪氨酸 2. 由分支酸形成色氨酸 （二）组氨酸的生物合成 P356 four steps three steps one step one step four steps two steps two steps The biosynthesis of all aromatic amino acids share the first seven steps of reactions P356 The 2nd PEP enter here Ring formation step 1st double bond 2nd double bond Chorismate Chorismate, formed from the condensed product of PEP and erythrose 4-P, is the common precursor of Trp, Tyr and Phe. P356 Chorismate is converted to Trp by accepting an amino group from Gln, two carbons from 5 phosphoribosyl- 1-pyrophosphate (PRPP), and three carbons from Ser. (邻氨基苯甲酸 ) Synthase Transferase Isomerase Synthase Trp Synthase P358 Chorismate can also be converted to prephenate which serve as the common precursor of Phe and Tyr biosynthesis Claison rearrangement Chorismate mutase Dehydrogenase dehydratase P357 Transferase Hydrolase The synthesis of histidine begins with the condensation of PRPP and ATP: The C-1 of the ribose ring is linked to the N-1 of the purine ring. Gln and Glu. P359 四、氨基酸生物合成的调节 （一）通过终端产物对氨基酸生物合成的抑制 1. 简单的终端产物抑制 2. 不同终端产物对共经合成途径的协同的抑制 3. 不同分支产物对多个同工酶的特殊抑制 4. 连续产物抑制 （二）通过酶生成量的改变调节氨基酸的生物 合成 P361 The first case of allosteric feedback inhibition was discovered in studying Ile synthesis in E. coli Several intricate feedback inhibition mechansims have been found in branched pathways for amino acid biosyntheses Sequential Concerted Enzyme multiplicity High level of one (e.g., Y) should not prevent the synthesis of the other (e.g., Z). In branching pathways leading to the synthesis of multiple end products from common precursors, several forms of feedback inhibitionmechanisms are used to coordinately regulate the synthesis of all the amino acids. 五、氨基酸转化为其它氨基酸及其它代谢物 （一）氧化氮的形成 脊椎动物体内的一种重要的信息分子，在 信号传导过程中起重要作用。它是由精氨酸在 氧化氮合酶（NOS）的催化下形成的，产