Soto Biochem 10/13, 10/15
Soto Biochem 10/13, 10/15 CHEM 351
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This 3 page Class Notes was uploaded by Kayli Antos on Friday October 16, 2015. The Class Notes belongs to CHEM 351 at Towson University taught by Ana Soto in Summer 2015. Since its upload, it has received 11 views. For similar materials see Biochemistry in Chemistry at Towson University.
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Date Created: 10/16/15
Biochemistry Soto Fall 2015 o Enzymes n Uncompetitive Inhibitors N N 22 22 22 22 22 They do not bind at the active site but rather at a remote site and they only bind to the ES complex The Vmax is decreased because some of the ES complex is converted to ESI which is unable to convert the substrate to product The KM also decreases because the formation of ESI causes the equilibrium of E S ltgt ES to shift to the right Increasing the substrate concentration will not reverse these effects because the enzyme binds at a different site Vmax5 The MM equation IS changed correCted to V0 KMa S 1 KM CU V o VmaxS Vmax An uncompetitive inhibitor changes the x and y intercepts of a double reciprocal plot The y intercept is d Nmax and the x intercept is d KM Mixed Inhibitors N N 22 22 22 They bind at a different sit than the active site but are able to bind to the lone enzyme or the ES complex It is called a noncompetitive inhibitor when it binds to both the E and ES complex with the same affinity but this is rare It affects only Vmax and not KM When the affinities are different then it is a mixed inhibitor and affects both the Vmax and KM values Vina acts i W a aKMwS V0 Vmax5 The slope and x and y intercepts are all changed by mixed inhibitors Slope is dKMVmax y intercept is d Nmax and x intercept is d dKM Noncompetitive inhibitors only change the slope and y intercept The MM equation is V0 2 Vmax Review Kt v25 Competitive T Uncompetitive l l Mixed Tl l Noncompetitive l Catalytic Power Of Enzymes N N Enzymes can accelerate the rate of the reaction by 517 orders of magnitude There are two ways that enzymes achieve catalysis Covalent Many types of chemical reactions take place between the functional groups of the enzyme and substrate The covalent 1 1 interactions occur at the active site and lower the activation energy of the reaction be providing an alternative reaction pathway NonCovalent A lot of the energy needed to lower the activation energy comes from the formation of noncovalent interactions between the substrate and enzyme like hydrophobic interactions or hydrogen bonding As each weak interaction forms some energy is released which stabilizes the interaction 9W z An enzyme with a structure completely complementary to its substrate would be a poor catalyst To be most effective an enzyme should be complementary to the transition state Some weak interactions are formed with the substrate but interactions are optimized with the TS z Even while interacting with the enzyme the TS is not stable Binding Energy z V kS z The energy released by noncovalent interactOions forms is enough to offset the energy needed to reach the TS Entropy Reduction z Molecules in solution have freedom of movement AS which reduces the possibility of successful collisions Enzymes and binding energy work to properly orient the substrates so they re able to react z Enzymes stabilize the TS by lowering its energy and they destabilize the S by increasing its energy WM z When the substrate is bound to the enzyme there are certain catalytic groups that are positioned so they help form bonds by different mechanisms General acid base catalysis Proton transfer to or from the substrate help stabilize charged intermediates Covalent catalysis Transient covalent bonds can form to provide an alternative reaction pathway with lower energy Metal ion catalysis lonic interactions can help properly orient the substrate or help to stabilize the TS Metals are also able to mediate redox reactions AcidBase Catalysis z General acidbase catalysis is specifically the proton transfers by weak acids or bases that aren t water z At the enzymes active site amino acid side chains function as proton donors or acceptors and are positioned so to allow this transfer Covalent Catalysis 22 22 For the reaction of AB 9 A B the covalent catalysis reaction is ABX9AXB9AXB z Many amino acids or functional groups from cofactors act as nucleophiles when forming covalent bonds with substrates Effect Of QH On Enzyme Activity z Enzymes reliance on pH to function is due to the fact that amino acids must maintain a certain ionization state to work If the graph of an enzymes activity vs pH is a bell curve there are at least two amino acids 22 22