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Regulation of metabolism on the cellular level

Regulation of metabolism on the cellular level. Vladimíra Kvasnicová. General Principles of Regulation. catabolic / anabolic processes last step of each regulation mechanism: change of a concentration of an active enzyme (= regulatory or key enzyme) regulatory enzymes

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Regulation of metabolism on the cellular level

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  1. Regulation of metabolism on the cellular level Vladimíra Kvasnicová

  2. General Principles of Regulation • catabolic / anabolic processes • last step of each regulation mechanism: change of a concentration of an active enzyme(= regulatory or key enzyme) • regulatory enzymes • often allosteric enzymes • catalyze higly exergonic reactions (irreverzible) • low concentration within a cell

  3. I. Regulation on the organism level • signal transmission among cells(signal substances) • signal transsduction through the cell membrane • influence of enzyme activity: • induction of a gene expression • interconversion of existing enzymes(phosphorylation / dephosphorylation)

  4. II. Regulation on the cell level • compartmentalization of mtb pathways • change of enzyme concentration(on the level of synthesis of newenzyme ) • change of enzyme activity(an existingenzyme is activated or inactivated)

  5. 1. Compartmentalization of mtb patways • transport processes between compartments • various enzyme distribution • various distribution of substrates and products ( transport) • transport of coenzymes • subsequent processes are close to each other

  6. Compartmentalization of mtb pathways The figure is found at http://fig.cox.miami.edu/~cmallery/150/proceuc/c7x7metazoan.jpg (May 2007)

  7. Cytoplasm • glycolysis • gluconeogenesis (from oxaloacetate or glycerol) • metabolism of glycogen • pentose cycle • synthesis of fatty acids • synthesis of nonessential amino acids • transamination reactions • synthesis of urea (a part; only in the liver!) • synthesis of heme (a part) • metabolism of purine and pyrimidine nucleotides

  8. Mitochondrion • pyruvate dehydrogenase complex (PDH) • initiation of gluconeogenesis • -oxidation of fatty acids • synthesis of ketone bodies (only in the liver!) • oxidation deamination of glutamate • transamination reactions • citrate cycle • respiratory chain(inner mitochondrial membrane) • aerobic phosphorylation(inner mitoch. membrane) • synthesis of heme (a part) • synthesis of urea(a part)

  9. Endoplasmic Reticulum Smooth ER • synthesis of triacylglycerols and phospholipids • elongation and desaturation of fatty acids • synthesis of steroids • biotransformation of xenobiotics • glucose-6-phosphatase Rough ER • proteosynthesis(translation and posttranslational modifications)

  10. Golgi Apparatus • posttranslational modification of proteins • protein sorting • export of proteins (formation of vesicules) Ribosomes • proteosynthesis Nucleus • replication and transcription of DNA • synthesis of RNA

  11. Lysosomes • hydrolysis of proteins, saccharides, lipids and nucleic acids Peroxisomes • oxidative reactions involving O2 • use of hydrogen peroxide • degradation of long chain FA (from C20)

  12. 2. Synthesis of new enzyme molecules: • induction by substrate or repression by product(on the level of transcription) examples: • xenobiotics  induction of cyt P450 • heme  repression of delta-aminolevulate synthase

  13. 3. Change of activity of an existing enzyme • in relation to an enzyme kinetics • concentration of substrates ( Km) • availability of coenzymes • consumption of products • pH changes • substrate specificity - different Km

  14. 3. Change of activity of an existing enzyme • activation or inactivation of the enzyme • covalent modification of the enzymes • interconversion: phosphorylation/dephosphorylation) • cleavage of an precursore (proenzyme, zymogen) • modulation of activity by modulators (ligands): • feed back inhibition • cross regulation • feed forward activation

  15. Phosphorylation / dephosphorylation • some enzymes are active in a phosphorylated form, some are inactive • phosphorylation: • protein kinases • macroergic phosphate as a donor of the phosphate (ATP!) • dephosphorylation • protein phosphatase • inorganic phosphate is the product!

  16. Reversible covalent modification: • A) • phosphorylation by a protein kinase • dephosphorylation by a protein phosphatase • B) • phosphorylated enzyme is either active or inactive (different enzymes are influenced differently) The figure is found at:http://stallion.abac.peachnet.edu/sm/kmccrae/BIOL2050/Ch1-13/JpegArt1-13/05jpeg/05_jpeg_HTML/index.htm (December 2006)

  17. Modulatorsof enzyme activity(activators, inhibitors) • isosteric modulation: competitive inhibition • allosteric modulation: • change of Km or Vmax • T-form (less active) or R-form (more active) • important modulators: ATP / ADP

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