enzymes dr arifullah [compatibility mode]
Post on 14-Jul-2015
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ENZYMESOutline
DefinitionCharacteristics of enzymes
Types of enzymesFactors 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. oxidoreductase2. transferase
3. hydrolase4. lyase
5. isomerase6. ligase
• Function: catalyzes oxidation-reduction reactions• e.g. alcohol dehydrogenase
• Other e.g. Biliverdin reductase; Glucose oxidase
• 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 4.1.2.5]; 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
Enzyme reaction…hypothesis
• lock and key hypothesis: proposed by Emil Fischer (1894)
perfect match like specific key & lock
• induced-fit hypothesis: proposed by Daniel Koshland
(1958) shows elasticity/flexibility
at active site well-accepted
Factors affecting enzyme activity
• enzyme concentration
• substrate concentration
• pH
• temperature
• inhibitors
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.
• 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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