FundamentalsScribe: Lauren Paul

Monday, August 24, 2009Proof: Kristina Hixson

Dr. DeLucasRegulatory StrategiesPage1 of 2

  1. Enzyme Regulation (Ch. 15) [S1]
  2. What Factors Influence Enzymatic Activity? [S2]
  3. The availability of substrate determines how fast the reaction will go. The rate is dependent on the substrate concentration. Often times the amount of enzyme equals the amount of substrate. So cells can be turned on to make additional enzymes. They do that to rapidly perform biological functions. As product accumulates the apparent rate of the reaction will decrease. The genetic regulation of enz synthesis and decay determines the amt of enzyme present at any given time.
  4. Remember all proteins have a half-life. Many different ways proteins are eliminated. One common way is by ubiquidaiting—places on protein where a series of enzymes adds ubiquitin and that targets proteins for degradation. All proteins go through this and anything that disrupts this process will have a dramatic effect on cells.
  5. Enzyme activity can be regulated by covalent modification by interconveratble enzymes with response time around 1 sec.
  6. allosetric interactions—Allo- “other”, some other place on enzyme is affected and by changing that interaction it changes usually the conformation of the enzyme in the active site.
  7. Covalent modification—protein kinases.
  8. Zymogens—totally inactive until something clips a portion of protein and activates it.An irreversible process.
  9. Isozymes—enzymes that are good in one tissue might in another tissue, with that same protein with a slightly different combination of subunits, give themdifferent activities and will give more or less of a product depending on the function of the tissue.
  10. Modulator proteins
  11. Transcription Regulation-not in PP
  12. The amount of enzyme synthesized in cell is determined by transcription regulation.
  13. Induction or repression.
  14. Genetic controls over enzyme levels have a response time of minutes to hours or even longer.
  15. Once synthesized, an enzyme can be degraded in different ways (like through specific mechanisms such as the ubiquitin mechanism).
  16. 3 diagrams we also don’t have… his research, not responsible
  17. Cys protease
  18. What Factors Influence Enzymatic Activity? [S3]
  19. What factors influence enzyme activity?
  20. Over-production—up-regulation and making more enzymes than you should (could lead to tumor formation because inhibits the tumor forming repressors).
  21. Reversible covalent modification—in this case, there is a protein phosphatase that phosphorylates a protein and puts a double negatively charged group on an enzyme, for example.
  22. What Factors Influence Enzymatic Activity? [S4]
  23. Zymogens are inactive precursors of enzymes. Specifically proteolytic cleavage produces an active enzyme. IN this case, looking at pro-insulin which is totally inactive. It is clipped in several places and what is left is two strands held together by only disulfide bonds which is now the active form of insulin.
  24. Just another way to control the activity of an enzyme is put it in your body as an inactive form and the body will activate it. Put it in a nonactive form can turn on clippage
  25. Figure 15.3 The proteolytic activation of chymotrypsinogen [S5]
  26. Chymotrpysinogen is precursor of a-chymotrypsin and is clipped to become active chymotrypsin—also held together by disulfide bonds.
  27. Proteolytic Enzymes of the Digestive Tract [S6]
  28. So these are just some zymogens and various active proteases.
  29. The Cascade of Activation Steps Leading to Blood Clotting [S7]
  30. Blood-clotting—there is a cascade that leads to the final affect. The intrinsic and extrinsic pathways converge at factor A;then the final common pathway involves activation of thrombin which cleaves Arg-Gly peptides and converts fibrinogen which gets clipped and aggregates into fibrin which clots blood.
  31. Shows intrinsic vs. extrinsic pathways. The difference is that one is mediated by various proteins and other is the interaction of blood itself to foreign surfaces that turns on the extrinsicpathway (2nd pathway)
  32. It’s a series of proteins where one affects the second one through allosteric interactions and eventually you get to final pathway.
  33. Point is to show you there is a complicated cascade that leads to final biological event.
  34. Isozymes Are Enzymes with Slightly Different Subunits [S8]
  35. Isozymes are a pain because when we crystallize things we need things the same because crystal has to be same thing packed over and over.
  36. Zymogens are the same protein but different subunits interact. You find different amounts of these and preponderants of one in one particular tissue versus another. Take the heart, for example—the heart is aerobic and uses lactate as a fuel converting it to pyruvate to fuel the citric acid cycle. It turns out for that conversion in the heart that the B4 is better than compared to in the muscle where A4 is used because glycolysis is required. So it depends on the biological role what form is used in what tissue.
  37. You have to look at many different tissues and how a drug affects them. It’s hard to prove you have a good inhibitor to drug companies because you have to show it won’t cause harm to other tissues.
  38. Depending on particular zymogens you might find it works great for one thing but bad for another.
  39. What are the General Features of Allosteric Regulation? [S9]
  40. He read the slide verbatim.
  41. What are the General Features of Allosteric Regulation? [S10]
  42. Enzymes situated at key steps.
  43. Look at kinetics—not typical Micahelis-Menton equation. It has more of a sigmoid shape. When you have allosteric inhibition it’s a cooperative type binding. So it initial binding helps further binding occur more rapidly.
  44. Can Allosteric Regulation Be Explained by Conformational Changes in Proteins? [S11]
  45. Allosteric proteins can occur in R state and T state.
  46. No substrate: T state predominates.
  47. With substrate: R state predominates and is binded tightly and it shifts the equilibrium.
  48. The Symmetry Model for Allosteric Regulation is Based on Two Conformational States for a Protein [S12]
  49. Cartoons showing what he just said.
  50. The Symmetry Model for Allosteric Regulation is Based on Two Conformational States for a Protein [S13]
  51. Another cartoon.
  52. The Symmetry Model for Allosteric Regulation is Based on Two Conformational States for a Protein [S14]
  53. More About the MWC Model [S15]
  54. Heterotropic—molecules that affect the binding of something other than itself.
  55. Homotropic—enzymes regulated by their substrate.

[End 20 min]