动物生物化学动物生化专题（激素生化）

1、Biochemistry of Hormones12第一节 概 述 一、细胞间信息传递到类型：内分泌（远距分泌）神经分泌神经内分泌自身分泌外分泌：外激素3Communication by extracellular signals usually involves the following steps: Synthesis and release of the signaling molecule by the signaling cell;Transport of the signal to the target cell; Binding of the signal by a speci

2、fic receptor protein leading to its activation; Initiation of one or more intracellular signal-transduction pathways by the activated receptor; Specific changes in cellular function, metabolism, or development; Removal of the signal, which often terminates the cellular response.4Signaling Molecules

3、in Animals Operateover Various Distances5Cellular communication by means of cellular secretions6Patterns of Signaling Endocrine Paracrine Autocrine7激素作用的特点信使作用相对特异性高效放大作用（nM、pM级）激素间相互作用：协同、拮抗、允许8含氮激素 1. 蛋白质和肽类激素 2. 氨基酸衍生物类固醇激素脂肪酸衍生物二、激素的分类根据化学性质9松果体激素丘脑下部激素垂体前叶激素垂体后叶激素性腺和胎盘激素局部激素外激素根据产生部位10三、激素的合成、分

4、泌、转运行代谢激素的合成11激素的分泌1213激素的转运游离型结合型细胞内降解与葡萄糖醛酸或硫酸结合而排出激素的代谢14四、激素的作用及其机制促进生长和发育保证生殖控制细胞外液的稳态调节代谢过程调节消化活动参与应激和免疫反应激素的作用15 含氮激素的作用机制 类固醇激素的作用机制 甲状腺激素的作用机制激素的作用机制16Receptors17受体的特性Receptor饱和性高亲和力(affinity)强特异性信息传递作用上调(upregulation)/下调(downregulation)18Maximal Cellular Response toa Signaling Molecule May

5、 Not Require Activation ofAll Receptors19FIGURE 13-3 The maximal physiological response to many external signals occurs when only a fraction of the receptor molecules are occupied by ligand. In this situation, plots of the extent of ligand binding and of physiological response at different ligand co

6、ncentrations differ. Here 50% of the maximal physiological response is induced at a ligand concentration at which only 18% of the receptors are occupied. Likewise, 80% of the maximal response is induced when the ligand concentration equals the Kd value, at which 50% of the receptors are occupied.20S

7、ensitivity of a Cell to External Signals Is Determined by the Number of Surface Receptors21Binding Assays Are Used to Detect Receptors and Determine Their Kd Values22Shown here are data for insulin-specific receptors on the surface of liver cells. A suspension of cells is incubated for 1h at 4 with

8、increasing concentrations of 125I-labeled insulin. The amount of radioactivity bound to cells is measured. The total binding curve A represents insulin specifically bound to high-affinity receptors as well as insulin nonspecifically bound with low affinity to other molecules on the cell surface. The

9、 contribution of nonspecific binding to total binding is determined by repeating the binding assay in the presence of a 100-fold excess of unlabeled insulin, which saturates all the specific high-affinity sites. In this case, all the labeled insulin binds to nonspecific sites, yielding curve C. The

10、specific binding curve B is calculated as the difference between curves A and C.FIGURE 13-4 Binding assays for cell-surface receptors can determine the Kd for high-affinity ligands and the number of receptors per cell.23The synthetic ligand alprenolol, which binds with high affinity to the epinephri

11、ne receptor on liver cells (Kd 310-9M), is used to detect the binding of two low-affinity ligands, the natural hormone epinephrine (EP) and a synthetic ligand called isoproterenol (IP). Assays are performed with a constant amount of 3Halprenolol to which increasing amounts of unlabeled epinephrine o

12、r isoproterenol are added. In a plot of the inhibition of 3Halprenolol binding versus epinephrine or isoproterenol concentration the concentration of the competitor that inhibits alprenolol binding by 50% approximates the Kd value for competitor binding. The Kd for binding of epinephrine to its rece

13、ptor on liver cells is only 510-5 M and would not be measurable by a direct binding assay with 3Hepinephrine. The Kd for binding of isoproterenol, which induces the normal cellular response, is more than tenfold lower.FIGURE 10-5 Binding of low-affinity ligands to cell-surface receptors can be detec

14、ted in competition assays.24FIGURE 10-6 Functional expression assay can identify a cDNA encoding a cell-surface receptor. Target cells lacking receptors for a particular ligand (X) are stably transfected with a cDNA expression vector encoding the receptor. The design of the expression vector permits

15、 selection of transformed cells from those that do not incorporate the vector into their genome. 25G蛋白Guanine nucleotide-binding regulatory protein(, , )26Diversity of G Protein-Coupled Receptor Signal Transduction Pathways 2728G ProteinCoupled Receptors That Activate or Inhibit Adenylyl Cyclase29第二

16、信使之一cAMP30FIGURE 13-7 Four common intracellular second messengers.The major direct effect or effects of each compound are indicated below its structural formula. Ca2+ and several membrane-bound phosphoinositides also act as second messengers.31Adenylyl Cyclase Is Stimulated and Inhibited by Differen

17、t Receptor-Ligand Complexes32FIGURE 13-15 Hormone-induced activation and inhibition of AC in adipose cells. Ligand binding to Gs-coupled receptors causes activation of AC, whereas ligand binding to Gi-coupled receptors causes inhibition of the enzyme. The G subunit in both Gs and Gi proteins is iden

18、tical; the G subunits and their corresponding receptors differ. Ligand-stimulated formation of active GGTP complexes occurs by the same mechanism in both Gs and Gi proteins. However, GsGTP and GiGTP interact differently with AC, so that one stimulates and the other inhibits its catalytic activity. 3

19、3cAMP-Activated Protein Kinase A Mediates Various Responses in Different Cells34Cyclic Nucleotide Metabolism - cAMP 35激素通过第二信使刺激肝糖原水解36其它第二信使cGMP三磷酸肌醇（IP3)二酰甘油（DG）Ca 2+37Cyclic Nucleotide Metabolism - cGMP 38FIGURE 13-28 Synthesis of DAG and IP3 from membrane-bound phosphatidylinositol (PI). Each PI

20、 kinase places a phosphate (yellow circles) on a specific hydroxyl group on the inositol ring, producing the phosphoinositides PIP and PIP2. Cleavage of PIP2 by PLC yields DAG and IP3. 39Inositol 1,4,5-Trisphosphate (IP3) Triggers Release of Ca2+ from the Endoplasmic Reticulum40Signaling by Inositol

21、 Phospholipids 41Diacylglycerol (DAG) Activates PKC, Which Regulates Many Other Proteins42Cyclic nucleotide metabolism-cGMP4344NO is synthesized in endothelial cells in response to Ach and the subsequent elevation in cytosolic Ca2+. NO diffuses locally through tissues and activates an intracellular

22、NO receptor with GC activity in nearby smooth muscle cells. The resulting rise in cGMP leads to activation of PKG, relaxation of the muscle, and thus vasodilation. The cell-surface receptor for atrial natriuretic factor (ANF) also has intrinsic GC activity; stimulation of this receptor on smooth mus

23、cle cells also leads to increased cGMP and subsequent muscle relaxation. FIGURE 13-30 Regulation of contractility of arterial smooth muscle by NO and cGMP.454647类固醇激素的作用机理484950Signal transduction pathways involved in prolactin regulation51Glucocorticoid receptor signaling52T3的作用机理5354细胞信号转导Physical

24、 signal transduction: light, sound, radiation, gravity, temperature, moisture,magnetic field.Chemical signal transduction Direct: physical, intercellular channels Indirect: local mediator, hormones, neurotrnasmitters55胞内信号转导机制 cAMP-PKA pathway cGMA-PKG pathway PI-PKC pathway Ca 2+ -calmodulin pathwa

25、y56信号转导的基本规律 放大作用 信号的通用性和特异性 信号转导的激活和失活 信号系统间存在交互作用 细胞对信号的反应可快可慢57FIGURE 13-18 Amplification of an external signal downstream from a cell-surface receptor. Binding of a single epinephrine molecule to one Gs proteincoupled receptor molecule induces synthesis of a large number of cAMP molecules. Four

26、cAMP activate two molecules of PKA, but each activated PKA phosphorylates and activates multiple product molecules. This second level of amplification may involve several sequential reactions in which the product of one reaction activates the enzyme catalyzing the next reaction. 58The Mitogen-activa

27、ted Protein Kinase (MAPK) Cascades 5960NPY Inhibition of Catecholamine Release 6162Cytokines, Growth Factors and Hormones 63Cytokines, Growth Factors and HormonesCytokines, growth factors (GF), and hormones are all chemical messengers that mediate intercellular communication. The regulation of cellu

28、lar and nuclear functions by cytokines, growth factors, and peptide or protein hormones is initiated through the activation of cell surface receptors (Rc). All receptors have two main components: 1) a ligand-binding domain that ensures ligand specificity and 2) an effector domain that initiates the

29、generation of the biological response upon ligand binding. The activated receptor may then interact with other cellular components to complete the signal transduction process. Many growth factors bind to receptors that are linked through G-proteins to membrane-bound phospholipase C (PLC). Activation

30、 of PLC cleaves phosphatidylinositol 4,5-bisphosphate (PIP2) to form diacylglycerols (DAG) and D-myo-inositol-1, 4, 5-trisphosphate (IP3). IP3 regulates intracellular Ca2+ by binding to the IP3 receptor on the endoplasmic reticulum (ER) and stimulating Ca2+ release from the ER. Free intracellular Ca

31、2+ can bind to calmodulin, and this Ca2+-calmodulin complex, in the presence of cyclic-AMP (cAMP), activates protein kinase A (PKA) by binding to the regulatory subunit of the enzyme. DAG binds to and activates protein kinase C (PKC). Other hormone receptors may be linked through G-proteins to adeny

32、l cyclase (AC) instead of PLC. Activation of AC increases the cellular levels of cAMP and, in the presence of the Ca2+-calmodulin complex, will activate PKA. Additionally, some growth factor and cytokine receptors are protein tyrosine kinases (PTK) that are directly activated by ligand-receptor inte

33、raction. Activation of any of the protein kinases, PKA, PKC, or PTK, catalyzes the phosphorylation of other proteins within the cell. Enzymes that are activated or inhibited by phosphorylation may mediate functional processes within the cell, while others may be one step in a protein kinase cascade that regulates nuclear events.Steroid hormones (i.e. estrogen, glucocor