細(xì)胞08年課件-32208第3章c minimizer

1、3.4.2 Transport protein離子載體(Ionophores) 由微生物產(chǎn)生的脂溶性抗生素。纈氨霉素(Valinomycin)由12個(gè)氨基酸組成的環(huán)狀肽；一種可動(dòng)離子載體(mobile ion carrier),插入脂質(zhì)體后，能特異性運(yùn)輸K+ ,使運(yùn)輸速率提高100 000倍。短桿菌肽 A (Gramicidin A)一種形成通道的離子載體(channel forming carrier)；由15個(gè)氨基酸組成的線性肽, 兩個(gè)分子在一起形成跨膜的通道；它能夠有選擇地將單價(jià)陽(yáng)離子按電化學(xué)梯度通過(guò)膜，但并不顯著提高運(yùn)輸速度；可被短桿菌肽 A離子通道運(yùn)輸?shù)年?yáng)離子有H+ NH4+ K+

2、Na+ Li+。Mobile Carrier and Channel Former3.5 Active Transport3.5.1 主動(dòng)運(yùn)輸?shù)奶攸c(diǎn)Active transport depends on integral membrane proteins that selectively bind a particular solute and move it across the membrane in a process driven by changes in the proteins conformation; ？Movement of a solute against a grad

3、ient requires the coupled input of energy ; ？The endergonic movement of ions or other solutes across the membrane against concentration gradient is coupled to an exergonic process, such as the hydrolysis of ATP, the absorbance of light, the transport of electrons, or the flow of other substances dow

4、n their gradients. ？幾種常見(jiàn)的主動(dòng)運(yùn)輸泵 Na+-驅(qū)動(dòng)的葡萄糖泵 腎和腸細(xì)胞的表面質(zhì)膜Na+-H+交換泵 動(dòng)物細(xì)胞的質(zhì)膜Na+-K+泵 大多數(shù)動(dòng)物細(xì)胞的質(zhì)膜Ca2+泵(Ca2+ ATPase) 真核細(xì)胞的質(zhì)膜 H+泵(H+ ATPase) 植物、真菌和某些細(xì)菌 的質(zhì)膜H+泵(H+ ATPase) 動(dòng)物細(xì)胞的溶酶體膜、 植物細(xì)胞的液泡膜細(xì)菌視紫菌素 某些細(xì)菌的質(zhì)膜 動(dòng)物細(xì)胞和植物細(xì)胞 主動(dòng)運(yùn)輸?shù)谋容^動(dòng)物細(xì)胞質(zhì)膜上有Na+-K+ ATPase，并通過(guò)對(duì)Na+、K+ 的運(yùn)輸建立細(xì)胞的電化學(xué)梯度； 植物細(xì)胞質(zhì)膜中沒(méi)有Na+-K+ ATPase，代之的是H+-ATP酶，并通過(guò)對(duì)H+的

5、運(yùn)輸建立細(xì)胞的電化學(xué)梯度(細(xì)菌、真菌也是如此)；在動(dòng)物細(xì)胞溶酶體膜和植物細(xì)胞的液泡膜上都有H+-ATP酶，它們作用都一樣，保持這些細(xì)胞器的酸性。動(dòng)物、植物細(xì)胞主動(dòng)運(yùn)輸?shù)谋容^主動(dòng)運(yùn)輸與被動(dòng)運(yùn)輸?shù)谋容^3.5.2 Transport ATPase ( pump)P-type ATPaseNa+-K+pump, Na+-K+ ATPase又稱Na+泵或 Na+/K+交換泵，或Na+ -K+ ATP酶；Na+-K+ ATPase是由兩個(gè)大亞基(亞基)和兩個(gè)小亞基(亞基)組成；亞基是跨膜蛋白，在細(xì)胞質(zhì)面有ATP結(jié)合位點(diǎn)，細(xì)胞外側(cè)有鳥(niǎo)本苷(ouabain)結(jié)合位點(diǎn);在亞基上有Na+和K+結(jié)合位點(diǎn)。鈉-鉀泵的

6、結(jié)構(gòu)鈉鉀泵工作原理Ca2+ pump, Ca2+ ATPaseThe Ca2+ -ATPase present in both the plasma membrane and the membranes of the endoplasmic reticulum. Ca2+ 泵的工作原理類似于Na+ -K+ 泵: 在細(xì)胞質(zhì)面有同 Ca2+結(jié)合的位點(diǎn)，一次可以 結(jié)合兩個(gè) Ca2+，Ca2+結(jié)合后使酶激活，并結(jié)合 上一分子 ATP，伴隨著 ATP 的水解酶被磷酸 化，Ca2+泵構(gòu)型發(fā)生改變，結(jié)合Ca2+的轉(zhuǎn)到細(xì) 胞外側(cè)被釋放，此時(shí)酶發(fā)生去磷酸化，構(gòu)型恢 復(fù)到原始的靜息狀態(tài)。Structure of

7、Ca2+ ATPaseCa2+-ATP酶激活機(jī)制Ca2+/鈣調(diào)蛋白復(fù)合物的作用 當(dāng)細(xì)胞內(nèi)Ca2+濃度升高時(shí)，Ca2+同鈣調(diào)蛋白 結(jié)合，形成活性復(fù)合物，該復(fù)合物同抑制 區(qū)結(jié)合，釋放激活位點(diǎn)，泵開(kāi)始工作。蛋白激酶C的作用 蛋白激酶C使抑制區(qū)磷酸化，從而解除抑制 作用；由上可以看出，在Ca2+-ATP酶的羧基端有三 個(gè)功能位點(diǎn)(區(qū)域)同激活位點(diǎn)結(jié)合區(qū)、同 CaM結(jié)合區(qū)、磷酸化位點(diǎn)。 Ca2+-ATP酶作用機(jī)理？H+/K+ ATPaseThe epithelial lining（粘膜上皮） of the stomach also contains a P-type pump, the H+/K+ -A

8、TPase, which secretes a solution of concentrated acid (up to 0.16 N HC1) into the stomach chamber. In the resting state, these pump molecules are situated in cytoplasmic membranes of the parietal cells（腔壁細(xì)胞）of the stomach lining and are nonfunctional. When food enters the stomach, a hormonal message

9、 is transmitted to the parietal cells that causes the pump-containing membranes to move to the apical cell surface, where they fuse with the plasma membrane and begin secreting acid In addition to functioning in digestion, stomach acid can also lead to heartburn. Control of acid secretion in the sto

10、machV-type pumps V-type pumps utilize the energy of ATP without forming a phosphorylated protein intermediate；V-type pumps actively transport hydrogen ions across the walls of cytoplasmic organelles and vacuoles (hence the designation V-type) ；V-type pumps occur in the membranes that line lysosomes,

11、 secretory granules, and plant cell vacuoles；V-type pumps have also been found in the plasma membranes of a variety of cells. For example, a V-type pump in the plasma membranes of kidney tubules helps maintain the bodys acid-base balance by secreting protons into the forming urine.F-type ATPases: 存在

12、于線粒體內(nèi)膜、植物內(nèi)囊體 膜和多數(shù)細(xì)菌質(zhì)膜上,運(yùn)輸方式是 H+濃度梯度運(yùn)動(dòng), 將釋放的能量同ATP合成偶聯(lián)起來(lái)。實(shí)際上前兩種質(zhì)子泵都屬于 H+離子泵，最后一種是F1-F0-ATP酶。F-type ATPases3.5.3 伴隨運(yùn)輸(Cotransport)兩種類型的主動(dòng)運(yùn)輸3.5.3 協(xié)同運(yùn)輸(Cotransport)協(xié)同運(yùn)輸 又稱偶聯(lián)運(yùn)輸。這種運(yùn)輸需要先建立離子學(xué)梯度(Ion gradients)，在動(dòng)物細(xì)胞主要是靠Na+泵、在植物細(xì)胞則是由H+泵完成的。協(xié)同運(yùn)輸?shù)姆较蚍譃椋和騾f(xié)同(symport)： 動(dòng)物細(xì)胞的葡萄糖和氨基酸就是與Na+ 同向協(xié)同運(yùn)輸。反向協(xié)同(antiport)： H+

13、 與Na+ 的反向協(xié)同。協(xié)同運(yùn)輸?shù)姆较駽otransport3.5.4 Active Transport in Bacteria cellsPhosphorylating transport 又稱基團(tuán)轉(zhuǎn)移(group translocation)機(jī)理： 是通過(guò)對(duì)被轉(zhuǎn)運(yùn)到細(xì)胞內(nèi)的分子進(jìn)行共價(jià)修飾,使其在細(xì)胞中始終維持“較低”的濃度；系統(tǒng)涉及幾種酶和一種稱為HPr的小分子蛋白質(zhì)；被轉(zhuǎn)移的基團(tuán)是磷酸烯醇式丙酮酸的高能磷酸鍵上的磷酸基團(tuán)；磷酸化的是被運(yùn)輸?shù)奈镔|(zhì)；運(yùn)輸中所需要的能量則由磷酸烯醇式丙酮酸的高能磷酸鍵所提供。過(guò)程:Phosphorylating transportBacteriorhodop

14、sin proton pump是光能驅(qū)動(dòng)的運(yùn)輸H+質(zhì)子泵是一種厭氧菌的膜蛋白：該蛋白含有七個(gè)螺旋，每個(gè)螺旋長(zhǎng)3-4nm；在蛋白質(zhì)的中部有能夠吸收光的視黃醛基團(tuán)(retinal group)，又稱發(fā)色基團(tuán);當(dāng)視黃醛基團(tuán)吸收光時(shí)，能引起整個(gè)分子的構(gòu)象發(fā)生變化，導(dǎo)致H+從細(xì)胞內(nèi)運(yùn)送到細(xì)胞外,造成細(xì)胞內(nèi)外的H+質(zhì)子濃度差。Bacteriorhodopsin proton pump細(xì)菌視紫紅質(zhì)可能的運(yùn)輸機(jī)制運(yùn)輸ATP酶(transport ATPases)運(yùn)輸ATP酶是一大類運(yùn)輸?shù)鞍?，該酶最早在?xì)菌中發(fā)現(xiàn)。E.coli具有兩層膜，運(yùn)輸ATP酶位于細(xì)菌的內(nèi)膜。運(yùn)輸ATP酶運(yùn)輸時(shí)需要水解ATP提供能量。運(yùn)輸

15、ATP酶主要參與糖、氨基酸和小肽的運(yùn)輸。32The auxiliary transport system associated with transport ATPases in bacteria with double membranes. A small section of the double membrane of E.coli bacterium34 The transport ATPases in the bacterial plasma membrane belong to the largest and most diverse family of ABC transport

16、er superfamily;Each member contains two highly conserved ATP-binding cassettes;ATP binding leads to dimerization of the two ATP-binding domains, and ATP hydrolysis leads to their dissociation; In this way, ABC transporters use ATP binding and hydrolysis to transport molecules across the bilayer; In E. coli ,78 genes encode ABC transporters .35 The transporter consists of four domains: two highly hydrophobic domains,each with six putative membrane-spanning segments that somehow form the translocation pathway; two ATP-binding catalytic domains (or ca