【正文】 l circumstances, the dietary proteins are almost pletely digested to their constituent amino acids, and these end products of protein digestion are rapidly absorbed from the intestine into the portal blood 2022/10/23 17 ? Amino acids are transported through the brush border by the carrier protein and it is an active transport 1. The classification of carrier protein: aciditic。2022/10/23 1 Amino Acid Metabolism 2022/10/23 2 論述題 （查資料課外完成） ?論述小兒偏食的害處 ?概述體內(nèi)氨基酸的來源和主要代謝去路 ?論述一碳單位的代謝及生理作用 2022/10/23 3 【 目的與要求 】 ? 掌握脫氨基作用、 氨的來源、去路 ，氨的轉(zhuǎn)運(yùn) …… ? 掌握尿素合成的部位和全過程 ? 掌握 一碳單位 的概念、來源、載體和功能 ? 需要掌握的概念： 必需氨基酸、蛋白質(zhì)的互補(bǔ)作用、氨基酸庫、脫氨基作用、 SAM、 PAPS…… 2022/10/23 4 outline 1. The nutrition of protein 2. The digestion、 absorption and putrefaction（ 腐爛作用） of protein 3. The general metabolism of AA 4. Metabolism of ammonia 5. Individual AA metabolism 2022/10/23 5 Section 1 The nutrition of protein ? Nitrogen balance ? The requirements ? Classification of amino acids 2022/10/23 6 Nitrogen balance ? Zero or total nitrogen balance: the intake = the excretion (adult) Amount of nitrogen intake is equal to the amount of nitrogen excreted is zero or total nitrogen balance ? Positive nitrogen balance: the intake the excretion during pregnancy, infancy, childhood and recovery from severe illness or surgery ? Negative nitrogen balance: the intake the excretion following severe trauma, surgery or infections. Prolonged periods of negative balance are dangerous and fatal if the loss of body protein reaches about onethird of the total body protein 2022/10/23 7 The requirements ? The requirements of protein for the health: the minimal requirement of protein is 30~50 gram for the adult ? Advice: 80 gram/day (中國營養(yǎng)學(xué)會(huì) ) ? ? ? 2022/10/23 8 ? nonessential amino acids can be synthesized by an anism usually are prepared from precursors in 12 steps ? Essential amino acids *** cannot be made endogenously must be supplied in diet eg. Leu, Phe….. Classification of amino acids 2022/10/23 9 Nonessential Essential Alanine Arginine* Asparagine Histidine * Aspartate Valine Cysteine Lysine Glutamate Isoleucine Glutamine Leucine Glycine Phenylalanine Proline Methionine Serine Threonine Tyrosine Tyrptophan *The amino acids Arg, His are considered “conditionally essential” for reasons not directly related to lack of synthesis and they are essential for growth only 攜來一兩本淡色書 2022/10/23 10 nutritional value ? Legumes(豆類 ) poor in Trp, but rich in Lys。 Cereals (谷類 ) poor in Lys, but rich in Trp ? Mutual plementation of amino acids ? Protein deficiencykwashiorkor, generalized edema and liver enlargement, abdomen bulged ? Suggestion: the binedaction of protein in diet 2022/10/23 11 Section 2 The digestion、 absorption and putrefaction of protein 2022/10/23 12 ? Proteins are generally too large to be absorbed by the intestine and therefore must be hydrolyzed to the amino acids ? The proteolytic enzymes responsible for hydrolysis are produced by three different ans: the stomach、 pancreas and small intestine (the major an) Digestive Tract of protein 2022/10/23 13 Stomach ? HCl (parietal cells ) and Pepsinogen (chief cells ) ? The pH of gastric juice is around . Food is retained in the stomach for 24 hrs ? HCl kills microanisms, denatures proteins, and provides an acid environment for the action of pepsin ? Autocatalysis: pepsinogen is converted to active pepsin(Pepsin A) by HCl ? Pepsin coagulates milk in presence of Ca2+ ions 2022/10/23 14 Pancreas and small intestine ? Endopeptidase (pancreas) Trypsin（ 胰蛋白酶 ） : carbonyl of arg and lys Chymotrypsin(糜蛋白酶 ） : carbonyl of Trp, Tyr, Phe, Met, Leu Elastase（ 彈性蛋白酶 ） : carbonyl of Ala, Gly, Ser Exopeptidase (pancreas) Carboxypeptidase A:除脯 、 精 、 賴氨酸之外的 C端 Carboxypeptidase B: amino side of Arg, lys in Cterminal ? Aminopeptidase (small intestine): cleaves Nterminal residue of oligopeptidaes Dipeptidase (small intestine) 2022/10/23 15 NH 2 CH C N H C H R 1OR 2 N H CH C N H C H R 3OR 4 N H CH C N H CHR 5OR 6C O O Haminopeptidase endopeptidase carboxypepidase NH 2 CH C N H CHORC O O HR39。 basic。 ?All intermediate products accelerate the reaction ?ratelimiting enzyme of urea cycle is argininosuccinate synthetase(精氨酸代琥珀酸合成酶 ) 2022/10/23 55 ?Hyperammononemia: ammonia intoxication tremors, slurring of speech, and blurring of vision, a/death ?Cause by cirrhosis(硬化 )of the liver or geic deficiencies Hyperammonemia and the