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MSU BCH 380 - Mechanisms of Enzymes or How do they catalyze chemical reactions?
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BCH 380 1st Edition Lecture 15 Outline of Last Lecture II. Inhibitors Cont.III. Allosteric Enzymesa. And RegulatorsOutline of Current Lecture IV. Mechanisms of EnzymesV. Enzyme Catalysts Current LectureChapter 6 – Mechanisms of Enzymes or How do they catalyze chemical reactions?- First, look at a generic chemical reaction, no enzyme- It is important to remember the intermediate is not usually long lived. It may exist for only a few instants before rearranging to give the product, though in some cases it can be stabilized for long periods of time that allow us to detect it Nomenclature: When a C atom loses a proton (H+), then both electrons stay on the carbon, which then negatively charged and is call a carbanion. When a C atom loses a hydride ion )H: or H-), it becomes positively charged and is called a carbocation. For reactions with a high energy barrier, energy in the form of heat must be provided in orer for the reaction to proceed. Enzymatic catalysis of the reaction A + B  A – B - Several principles are at play, two of these are substrate destabilization and transition state stabilization An enzyme binds to the transition state more tightly that it binds to substrates. The active site cavity of an enzyme generally contain a few polar ionizable residues- These residues make up much of the catalytic center of the enzyme- They are involved in substrate recognition or catalysis - This is one reason that histidine, cysteine, and aspartate are so over represented among active site residues Let B: represent a general base, reasy to accept a proton. Once it accepts or abstracts the proton, it is converted into H-B+- It is critical to note that H-B+ is no longer a base- In fact, it has been converted into the conjugate acid; it can now act as a proton donor.The ability to abstract or donate protons can significantly speed up many reactionsA – X + E  X – E + A- The enzyme bound intermediate is liberated as it reacts with a second substrate How is site directed mutagenesis done?- A synthetic oligonucleotide pH affects enzymatic ratesTriose phosphate isomerase interconverts dihydroxyacetone phosphate- An extremely fast enzyme whose rate is limited by how quickly the substrate can diffuse into the active site and how quickly the product can diffuse out of the active site (diffusion controlled


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MSU BCH 380 - Mechanisms of Enzymes or How do they catalyze chemical reactions?

Type: Lecture Note
Pages: 2
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