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Enzymes dr arifullah 2

Enzymes dr arifullah 2






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    Enzymes dr arifullah 2 Enzymes dr arifullah 2 Document Transcript

    • 1 ENZYMES Outline Definition Characteristics of enzymes Types of enzymes Factors effecting enzyme activity The definition & Characteristics of enzymes • A protein that acts as a catalyst, speeding the rate at which a biochemical reaction proceeds. a type of protein Characters: • a catalyst • Effective in smaller quantities • efficient and specific • reaction can be reversed • activities affected by surroundings • need helpers – cofactors/prostethic grps • involve in multiple steps of biochemical pathways Classification of enzymes  6 main classes according to International Union of Biochemistry and Molecular Biology (IUBMB): 1. oxidoreductase 2. transferase 3. hydrolase 4. lyase 5. isomerase 6. ligase • Function: catalyzes oxidation-reduction reactions • e.g. alcohol dehydrogenase • Other e.g. Biliverdin reductase; Glucose oxidase
    • 2 • Function: catalyzes reactions involving transfer of functional groups • e.g. Hexokinase • Other e.g. Glycoaldehyde transferase; DNA nucleotidylexotransferase • Function: catalyzes hydrolytic reactions involving use of water mol. • e.g. Triacylglycerol lipase • Other e.g. -amino acid esterase; Oxaloacetase H2O • Function: catalyzes cleavage of C-C, C-O, C- N and other bonds by other means than by hydrolysis or oxidation • e.g. Lysine decarboxylase • other e.g.: threonine aldolase [EC]; cystine lyase • Function: catalyzes intramolecular arrangement • e.g. Maleate isomerase • Other e.g. Inositol-3-phosphate synthase; Maltose epimerase] • Function: catalyzes the joining of two molecules with concomitant hydrolysis of the diphosphate bond in ATP or a similar triphosphate • e.g. Pyruvate carboxylase • Other e.g. GMP synthase; DNA ligase Enzyme as protein • exhibits characteristics like other proteins • primary structure  amino acid sequence e.g.: human pancreatic lipase (467 amino acids) N-Met1-…-Ser171-...-Asp194-...-His281-…-Cys467-C human trypsin (247 amino acids) N-Met1-…-His63-…-Asp107-…-Ser200-…-Ser247-C
    • 3 Lysozyme’s tertiary structure Anti-parallel -sheet (3) -helix (5) Aspartate carbamoyltransferase’s quartenary structure  2 catalytic trimers  3 regulatory dimers How enzyme reacts E + S ES E + P Enzyme reaction…hypothesis • lock and key hypothesis:  proposed by Emil Fischer (1894)  perfect match like specific key & lock
    • 4 • induced-fit hypothesis:  proposed by Daniel Koshland (1958)  shows elasticity/flexibility at active site  well-accepted e.g.: hexokinase reaction Factors affecting enzyme activity • enzyme concentration • substrate concentration • pH • temperature • inhibitors
    • 5 A B Change in pH effects the pull/push force of polar/nonpolar intramolecules which change the enzyme shape as well as active site – in acidic conditions, basic grps are protonized while in basic conditions, acidic grps are deprotonized. A C B
    • 6 • substances which bind to enzyme & disrupt the enzyme activity by blocking the production of ES-complex or E + P • reversible & irreversible • involves the noncovalent links between inhibitor and enzyme • 2 types:  competitive inhibitor  noncompetitive inhibitor  uncompetitive inhibitor Reversible inhibitors  competitive inhibitor  mol. similar to substrate  compete with substrate for active site e.g.: succinate dehydrogenase (E); succinate (S); malonate (I)  noncompetitive inhibitor  mol./ion attaches to second site (other than active site) at enzyme surface e.g.: prostaglandin synthase (E); arachidonate (S); aspirin (I)  uncompetitive inhibitor  binds to ES complex, forming an inactive ESI complex  e.g..: polymerase (E); nucleic acid (S); nevirapine (I) - HIV • covalently bonded – react with functional grp at active site, blocking active site from substrate rendering the enzyme inactive • mostly are toxic substances • e.g.: (see attached list) Irreversible inhibitors
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