9-29-07_lecture_plasmamem1

_lecture_plas - "Though force can protect in emergency only justice fairness consideration and cooperation can finally lead people to the dawn of

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: “Though force can protect in emergency, only justice, fairness, consideration and cooperation can finally lead people to the dawn of eternal peace.” Dwight D Eisenhower Miss Flamiel: We'll move on to science. Dot, what can you tell me about the great scientists of the nineteenth century? Dot: They're all dead. Miss Flamiel: No no no! Dot: All right. They're all living. Miss Flamiel: No no no! Yakko: Well, now we're getting into philosophy. -Animaniacs
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Announcements Quiz on glycolysis and kinetics available by noon today. Due by next Monday at noon. Written assignments due this Friday, October 3, at noon.
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Kinetic effects of inhibitors Vmax Km Active site Competitive Same Increases Occupied Non-competitive Decreases Same Not occupied
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Uncompetitive inhibitors Uncompetitive inhibitors bind only to ES complexes at locations other than the catalytic site. V max is decreased; K m is also decreased, so slope is the same. Differs from non-competitive inhibitors in that Km changes in un- competitive, but Km does not change
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Many pathways have allosteric product inhibition Allosteric means that it does not bind at the active site Figure shows example of allosteric feedback inhibition, used in many reaction pathways The end product allosterically binds to the enzyme to alter its conformation and inhibit it.
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Determination of the IC50 for an inhibitor IC50 is the [inhibitor] at which 50% of enzymatic activity has been inhibited Often plotted on a logarithmic scale Often sigmoidal function such as that shown above. It is important to use enough inhibitor concentrations to provide well- defined top and bottom plateau values. http://www.ncgc.nih.gov/guidance/section4.html
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Concerted allosteric mechanism 2 If a small amount of substrate is added to this solution it is more likely to bind to the R enzyme as this has a higher affinity. The combination of substrate with R-state enzyme removes some free R enzyme from the medium. This would pull the R/T equilibrium to the right. The result is positive substrate cooperativity - the binding of one substrate increases the ability of the enzyme to bind other substrates. Small amount substrate added As available [R] decreases, equilibrium shifts further to right Peter Birch, University of Paisley
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Mechanisms of Allostery The sequential hypothesis The sequential hypothesis assumes that the substrate has a more direct influence on the shape of the enzyme. In the absence of substrate the enzyme would exist more or less entirely in the T-form which has a very poor fit for the substrate. As the substate enters the active site, as usual by purely random collision, the enzyme protein moulds itself around the substrate to produce a good fit. This is known as induced fit . Each bound substrate makes subsequent substrate binding easier,
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This note was uploaded on 02/09/2010 for the course BIOL 230 taught by Professor Bartlett,e during the Fall '08 term at Purdue University-West Lafayette.

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_lecture_plas - "Though force can protect in emergency only justice fairness consideration and cooperation can finally lead people to the dawn of

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