06-Enzymes - Enzymes (March 21,2010)Enzymes: protein...

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Enzymes (March 21,2010)Enzymes: protein catalysts of biological systems Chemical transformations, interconversion of energy forms. High catalytic power and specificity. Active site: a particular site on the enzyme at which catalysis takes place. Proteins are good catalysts for many reactions because of their capacity to specifically bind a wide range of molecules. Utilization of the non-covalent forces. Optimally orients the substrates for bond forming or cleaving. Catalysis is achieved by stabilization of the transition state, the highest energy species in the reaction pathway.
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Rate Enhancement and Specificity Enzymes accelerate reaction by a million fold or more. Carbonic anhydrase: catalyzes the hydration of CO 2 , for the transfer of CO 2 from the tissue into the blood and then to the alveolar air, one of the fastest enzymes (10 6 s -1 ) with 10 7 rate enhancement. Enzymes are specific in both the reaction that is catalyzed and the choice of reactants (substrates). Enzymes usually catalyze a single reaction or a set of closely related reactions, rarely forming wasteful by-products. Proteolytic enzymes catalyze proteolysis (hydrolysis of a peptide bond,) and catalyze hydrolysis of esters, a related reaction. Proteolytic enzymes differ in substrate specificity. Subtilisin: indiscriminative. Trypsin (digestive): carboxyl side of K/R. Thrombin (blood clotting): cleaves Arg-Gly. DNA polymerase I, catalyzes DNA formation based on a template DNA with an error 1 in 10 8 . The specificity stems from precise interaction of substrate with the enzyme 3D structure. Trypsin Thrombin
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Cofactors Many enzyme catalytic activities depend on the presence of small molecules called cofactors. Apoenzyme: enzyme without its cofactor. Holoenzyme: catalytically active enzyme with cofactor. Cofactors: Metal ions Carbonic anhydrase requires Zn 2+ . Small organic molecules (conenzymes) Derived from vitamins Glycogen phosphorylase (mobilizes glycogen for energy) requires pyridoxal phosphate (PLP). If tightly bound, the coenzyme is called prosthetic group. If loosely bound, then more like cosubstrate. Enzymes that use the same coenzyme are usually mechanistically similar.
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The energy in reactants are converted with high efficiency into different forms in biochemical reactions. Photosynthesis: light energy into ion gradient into chemical-bond energy. Mitochondria: small molecules from food into ion gradient into adenosine triphosphate (ATP). Myosin: ATP into mechanical energy of muscle contraction. Pumps in membranes: ATP into chemical and electric gradients by transporting molecules and ions. Ca
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This note was uploaded on 11/10/2010 for the course CHE Biochem taught by Professor Disney during the Spring '10 term at SUNY Buffalo.

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06-Enzymes - Enzymes (March 21,2010)Enzymes: protein...

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