III. Chemical Characteristics and Synthesis of Bioregulators

1. III. Chemical Characteristics and Synthesis of Bioregulators Amino acids, amines, peptides and proteins Steroid Bioregulators Thyroid hormones Eicosanoids Other important regulators

2. Chemical Nature of Hormones • Peptide and protein hormones (most abundant): thyrotropin releasing hormone (TRH), gonadotropin releasing hormone (GnRH), growth hormone (GH), prolactin (PRL), insulin, insulin-like growth factor-I (IGF-I) etc. • Amino acid derivatives: thyroid hormone, epinephrine etc. • Steroid hormones: testosterone, estrogen & cortisone etc. • Lipids: prostaglandin, retinoic acid etc. • Nucleotides: cAMP, cytokinins, cGMP etc. • Oligosaccharides: a-1,4-oligogalacturonides (OGs) • Gases: CO, ethylene etc. • Ecosanoids: Derived from arachidonic acid; e.g., prostaglandins, leukotrienes (produced by leukocyte to cause inflammation in asthma) and thromboxanes (It acts in the formation of blood clots and reduce blood flow to the site of a clot)

3. [I] Catecholamines When an amine group is attached to a catechol, it is termed as a catecholamine catechol Examples of catecholamines are: Dopamine, epinephrine and norepinephrine Catecholamines are synthesized from tyrosine by neurons and cells of the adrenal medulla

4. Biosynthesis of Catecholamines Enzymes involved: • Tyrosine hydorxylase • Dopa decarboxylase • Dopamine b hydroxylase • Phenylethnolamine- N-CH3–transferase (PNMT) • Tyrosine hydroxylase immunoreactivity is frequently used as a biochemical marker to locate catecholamine-secreting cells • Catecholamines are more than just neurotransmitters, DA, NE and E can also be released into the circulation to function as hormones

5. Metabolism of Norepinephrine in the Central Nervous System • Release of catecholamine neurotransmitters is metabolised by: • MAO = monoamine oxidase • COMT = catechol-O-methyl transferase

6. [II] Indolamines and Melatonin Serotonin: 5’hyroxytrypamine NAT: N-acethltransferase HIOMT: Hydroxyindole-O-methyltransferase Melatonine: N-acetyl-5-methoxytryptamine L-aromatic amino acid decarboxylase Serving as neurotransmitter Melatonine is secreted from pineal gland primarily in the dark phase which is important in regulating cyclic functions and having negative inferences on thyroid and reproductive functions. Reading Assignment: Melatonin

7. [III] Steroid Bioregulators Steroid nucleus The Steroid Nucleus

8. Naturally Occurring Steroids

9. Estrogens and Androgens

10. Some Synthetic Steroids and Nonsteroids Isolated from plant, with estrogenic activity Synthetic estrogenic compound A potent synthetic glucocorticoid hormone Antagonist of estrogen receptor

11. Corticosteroids Progestens

12. Enzymes Involved in Steroid Synthesis • All vertebrate steroid bioregulators are synthesized from cholesterol which is synthesized from acetyl CoA • Steroidogenesis: synthesis of steroid nucleus from acetyl CoA • Key enzymes involved in synthesis of steroid bioregulators are: • CYP21: C24 hydrolase • CYP11A: Cholestrol side chain cleavage (20-22 Desmolase) • CYP17: 17a-hydroxylase, 17,20-Lyase • CYP19: Aromatase • CYP11B1: 11b-hydroxylase • CYP11B2: Alderstrone synthetase • CYP1A1: Aryl hydrocarbon hydroxylase • Steroid bioregulators in the circulation are bound to plasma binding proteins • Reading Assignment: Sex Hormone Binding Globulin

13. [IV] Thyroid Hormones • T3 and T4 are synthesized from tyrosine • Most thyroid hormones are bound to plasma proteins • Receptor molecules for T3 and/or T4 are nuclear receptors, two major isoforms, TRy-1 and TRb-1 • Tyrosine is first incorporated into a globular protein (thyroglobulin) and then iodinated by thyroid peroxidase to form DIT • Two DITs are to form T4 • Through deiodination at the outer ring, T3 is formed • T4 or T3 moieties are hydrolyzed from thyroglobulin and released into the circulation T3 or T4 are bound to plasma proteins in the circulation

14. [V] Insect Developmental Hormones a-ecdysone b-ecdysone: 20- hydroxy-ecdysone Ecdysone JH-I JH-II JH-III Juvenile Hormone

15. [VI] Eicosanoids (I) • Eicosanoids are small lipids derived from a common precursor, arachidomic acid • Eicosanoids include: prostaglandins, leukotrienes and throboxanes • Prostaglandin was discovered by Maurice Goldblatt of England and U.S. Von Euler of Sweden. By elucidating the biological importance and the biosynthetic pathway of prostaglandin, Sune Bergstrom, Bengt Samuellson and John Vane were awarded with Nobel Prize in Physiology and Medicine in 1982 • Postaglandins were first found in prostate gland, and subsequently found in many tissues of men and women • Prostaglandins exhibit diverse actions: stimulation of smooth muscle contraction in intestine and uterus, vasodilatation , and modulation of central nervous system function • Prostaglandins also stimulate synthesis of corticosteroids, testosterone and a variety of enzymes • PGF2a functions as uterine leuteolytic substance in certain mammals

16. [VI] Eicosanoids (II) • Prostaglandins also reduce progesterone synthesis by the corpus luteun, induce ovulation and lactation in rodents, and may be involved in induction of labor • Prostaglandins may induce inflammation and fever • Prostacyclin (PGI2) , another form of prostaglandin, is a potent inhibitor of blood platelet aggregation and inhibits blood clotting • Thromboxanes A2 causes translocation of free calcium ions to bring about changes associated with the shape of blood platelets to facilitate blood clotting • Leukotrines are synthesized and released by white blood cells in response to injury. They contribute to inflammation or allergic responses by causing contraction of vascular smooth muscle and by increasing vascular permeability. Increasing levels of leukotrines have been associated with allergic reactions, asthma, cystic fibrosis, septic shock and a number of other disorders

17. Prostaglandin Structures

18. Biosynthesis of Eicosanoids

19. [VI] Peptide and Protein Bioregulators • Peptide or protein bioregulator are encoded by genes • The mRNAs of peptide or protein bioregulators are translated on the endoplasmic reticulum membrane which as recognized by signal recognition particle and docking protein, and direct the pre-pro-peptide into the cisternae of the endocriplasmic reticulum • The signal peptide and the pro sequence are removed by proteolytic cleavage and the mature peptide is secreted out of the cell • For otherbioregulators that contain carbohydrates and/or lipids (e.g., GTHs or TSH), acetyl group or amide group, these components are added to the mature protein while is in the cisternae of the smooth endoplasmic reticulum or Golge Complex

20. Translation of Peptide or Protein Bioregulators

21. Post translational Processing of Proteins Reading Assignment: Processing in vitro of placental peptide hormone by smooth microsome

22. Structures of Insulin Family Proteins • This slide shows the structural homology among insulin family proteins • Insulin family proteins: insulin, insulin-like growth factor-I, insulin-like growth factor-II and relaxin

23. Primary Structures of Several Prohormones gMSH-CLIP = adrenalcor-ticotropin (ACTH) Somatostatin-28 more potent than Somatostatin-14 Neurophysin serve as a binding protein for the transport of ADH (vasopressin ) **Important Question Are the pro-hormone sequence biological active??

24. [VII] Other Important Bioregulators • Acetylcholine (Ach): • Serves as a major neurotransmitter in the peripheral nervous system and in the brain • It is synthesized from choline and acetate by choline acetyl-traansferase in the membrane of the postsynaptic cells • It functions by first binding to the acetylcholine receptor • Gamma-Aminobutyric Acid (GABA): • It functions as an inhibitory neurotransmitter • It is formed mainly from glutamate by glutamate decarboxylase • Interleukins: • Interleukins are secreted by lymphocytes and macrophages • Interleukins function in autocrine/paracrine fashion within the vascular system and several lymphatic tissues. • There are more than a dozen recognized interleukins. IL-1 can activate helper T-cell; IL-2, a mitogen secreted by helper T-cell which can stimulate B-cell to divide and form plasma cells, it also stimulate helper T-cells to proliferate; IL-6 is known to interact with adrenal cells to release cortisol • Helper T-cells also produce g-interferon which can transform macrophage to attach viral infected cells. Interleukin, g-interferon and cytokines are involved in immune responses

25. Other Important Bioregulators (II) • Retinoic acid is a metabolite of vitamin A (retinol) • It mediates the functions of vitamin A required for growth and development in chordate animals including all higher animals from fishes to humans • During early embryonic development, retinoic acid acts through Hox genes to determine the anterior/posterior axis of the animal

26. Reading Assignment (III) • Melatonin • Serotonin • Tamoxifen • Eicosanoid 5. C-peptide of pro-insulin 6. Processing in vitro of placental peptide hormone by smoth microsome 7. Nobel Lecture by Sune Bergstrom