Enzymes - Enzyme Classification Simple Enzymes: composed of...

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1 Simple Enzymes: composed of whole proteins Complex Enzymes: composed of protein plus a relatively small organic molecule holoenzyme = apoenzyme + prosthetic group / coenzyme Enzyme Classification A prosthetic group describes a small organic molecule bound to the apoenzyme by covalent bonds. When the binding between the apoenzyme and non-protein components is non-covalent, the small organic molecule is called a coenzyme. Oxidoreductases Act on many chemical groupings to add or remove hydrogen atoms. Transferases Transfer functional groups between donor and acceptor molecules. Kinases are specialized transferases that regulate metabolism by transferring phosphate from ATP to other molecules. Hydrolases Add water across a bond, hydrolyzing it. Lyases Add water, ammonia or carbon dioxide across double bonds, or remove these elements to produce double bonds. Isomerases Carry out many kinds of isomerization: L to D isomerizations, mutase reactions (shifts of chemical groups) and others. Ligases Catalyze reactions in which two chemical groups are joined (or ligated) with the use of energy from ATP. Enzymes Enzymes are protein catalysts Catalysts alter the rate of a chemical reaction without undergoing a permanent change in structure How can an enzyme reduce the activation energy? (1) Binding to the substrate can be done such that the formation of the transition state is favored (2) Orientation and positioning of substrate(s) (3) Bonds in the substrate can be ‘activated’ by functional groups in the catalytic site Active site is lined with residues and sometimes contains a co- factor Active site residues have several important properties: Charge [partial, dipoles, helix dipole] pKa Hydrophobicity Flexibility Reactivity Enzyme active site Free energy, G Intermediate State (A * ) Transition State G A G B Δ G 1 ° (A Æ A * ) Δ G 2 ° (A * Æ B) uncatalyzed reaction Reaction Coordinate A Æ A * Æ B - the activation energies for the formation of the intermediate state, and its conversion to the final product are each lower than the activation energy for the uncatalyzed reaction -intermediate state- resembles transition state but with lower energy, (due to interaction with a catalyst) - transition state defines free energy maximum state Δ G = Δ H -T Δ S activation energy is lowered during energy required for the reaction change in entropy (degree of conformational flexibility) during molecules often need to go through energy demanding (strained/distorted) conformations for reaction to take place Entropic and enthalpic factors in catalysis catalysis cannot be too large or else reaction will be slow reaction ‘solved’ by having an intermediate state that resembles the transition state but is of lower energy because of favourable binding to the catalyst
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2 Effect of Temperature Effect of pH Measuring Enzymatic Rates - ideally done with a system where the product or substrate absorb a particular wavelength of light - this depends on enzyme
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This note was uploaded on 10/16/2010 for the course CHEM 60280 taught by Professor Ryu during the Spring '09 term at TCU.

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Enzymes - Enzyme Classification Simple Enzymes: composed of...

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