BCHM 307 1st Edition Lecture 14 Outline of Last Lecture I Km and Velocity A Velocity Equation II Allosteric Enzyme Reactions A Sigmoidal Curve B Allosteric Chain Reaction III Enzyme Kinetics Graph A How to Plot the Graph B Reverse Reaction Outline of Current Lecture I Lineweaver Burk Plot II Enzyme Inhibitors A Irreversible Inhibitors III Reversible Inhibitors A Competitive Inhibitors B Non Competitive Inhibitors C Un Competitive Inhibitors IV How Enzyme Catalysis Works Current Lecture The Michaelis Menton graph will not allow you to properly estimate Km or Vmax due to its curved shape The graph can be turned into a linear form that will give you the true values of Km and Vmax This transformed graph is called the Lineweaver Burk plot or double reciprocal plot The graph plots 1 velocity versus 1 substrate concentration The line plotted has the standard line form of y mx b The slope is given by Km Vmax The y intercept is 1 Vmax and the x intercept is 1 Km Enzyme inhibitors are molecules that decrease the catalysis rate Enzyme inhibitors can be broken down into two categories reversible and irreversible Irreversible inhibitors are also called suicide inhibitors They covalently attach to the enzyme and completely inactivate it They can t inhibit another enzyme once attached though The covalent bond will modify the enzyme causing it to no longer by a catalyst This permanently modified enzyme is called a derivitized enzyme An example would be organoflurophosphates such as DIFP DIFP inhibits acetylcholinesterase and bonds with the serine residues in the active site These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Reversible inhibitors can be broken down into three groups competitive non competitive and uncompetitive Competitive inhibitors bind to and block the enzyme s active site temporarily The inhibitor looks very similar to the substrate allowing it to fit closely to the active site though not perfectly The Km will increase when this happens while the Vmax will stay the same This decreases the affinity of the substrate for the enzyme overall Increasing the substrate concentration will help to overcome these effects An example is malonate which is a competitive inhibitor of succinate dehydrogenase Atropine is another example which helps to break down acetylcholine to prevent chronic nerve stimulation Nom competitive inhibitors bind to another area on the enzyme besides the active site These inhibitors do not resemble the substrates In terms of enzyme kinetics the Km will say the same due to the inhibitor not binding to the active site The Vmax will decrease though Increasing the substrate concentration will not help to overcome these effects Uncompetitive inhibitors can only bind to the enzyme at a place other than the active site when the substrate is already bound to the enzyme The Km will decrease increasing the substrate concentration will not effect this either Certain functional groups are involved in enzyme catalysis Alpha amino and carboxyl groups cannot be involved because they are involved in peptide bonds Specific R groups are involved in catalysis including those of Asp Glu His Lys Ser Cys and Tyr When an inhibitor covalently binds to the enzyme it also binds to the active site amino acid residues This helps biochemists to understand what kind of chemistry is involved
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