Enzymes

1. Enzymes

2. Enzymes Large bio-molecules that increase the rate of reaction in living systems Enzymes act as catalyst – molecules that speed up a chemical reaction by lowering the activation energy

3. Enzymes • Most Enzymes are globular protein molecules • Other types such as ribozymes are common • Extremely effective causing reactions to be 109 to 1020 times faster • Extremely specific - each reaction catalyzed by only 1 enzyme • e.g. Trypsin: cleaves peptide linkages only on carboxyl side of lysine and arginine • Many enzymes are stereospecific:Arginase converts L-arginine to to L-ornithine but does not convert D-arginine

4. Enzymes • There are more than 3000 enzyme in a cell • Enzymes are distributed in the body relative to their need (digestive enzymes in stomach and pancreas) From Yahoo Images

5. Enzyme Nomenclature • Enzymes are typically given names based on the reactions they are involved in with most ending in …… ase • Lactate dehydrogenase • speeds up removal of H from lactate • Acid phosphatase • cleaves phosphate ester bonds under acidic conditions (some older ones do not end in “ase” like pepsin, trypsin, chymotrypsin)

6. Enzymes are classified into six major groups according to their reactions • 1. Oxidoreductases • catalyze oxidations and reductions • 2. Transferases • catalyze NH2, CH3, etc. from one molecule to another • 3. Hydrolases • catalyze hydrolysis reactions • 4. Lyases • catalyze addition of two group to make C=C or removes two atoms to create C=C • 5. Isomerases • catalyze isomerization reactions • 6. Ligases or Synthetases • catalyze joining of two molecules

7. Enzyme - Youtube • http://www.youtube.com/watch?v=AFbPHlhI13g

8. Enzyme Terms • Most enzymes are made of just a Polypeptide chain • Some enzymes have a nonprotein portion called a cofactor • The protein portion is called an apoenzyme • Cofactors = nonprotein portions = coenzyme • Metal Cofactors such as Zn2+, Mg2+ • an apoenzyme cannot catalyze a reaction withouth its cofactor

9. Enzyme Terms • Substrate = compound on which the enzyme “works” • Active site = specific portion of the enzyme where substrate binds

11. Enzyme Terms • Activation = process that makes an inactive enzyme active • Inhibition = any process that makes an enzyme less active or inactive • competitive vs. noncompetitive inhibition

12. Enzyme Activity • Enzyme and substrate concentration rate Enzyme concentration

13. rate Substrate concentration Enzyme Activity • Enzyme and substrate concentration maximum rate (enzyme saturation)

14. Enzyme Activity • Temperature – changes conformation rate 37o C Temperature

15. Temp Effect - youtube http://www.youtube.com/watch?v=3luXqXQpMGA

16. Enzyme Activity • pH – changes conformation or denatures rate 5.3 acidic pH basic

17. Denaturation - pH http://www.youtube.com/watch?v=-8PFb9dOR8c

18. Mechanism • Mechanism of Enzyme Activity • Highly specific • Enzyme-Substrate Complex • Lock and Key Model • rigid 3-D structure • fits exactly into active site • active site may have only1 or 2 AA, enzyme mayhave hundreds!

19. Mechanism • Mechanism of Enzyme Activity • Induced Fit Model • Daniel Koshland • some flexibility • shape changes to fitsubstrate • hand and glove analogy

20. Inhibitors Something that inhibits the enzymes ability to react • Competitive Inhibition • Inhibitor moleculetakes the active site • Substrate cannotreact at active site • Large concentrationsof substrate “overcome”inhibition(competitive)

21. Inhibitors Something that inhibits the enzymes ability to react • Noncompetitive Inhibition • Inhibitor molecule takes other than the active site • Enzyme structure ischanged - active siteis altered • Large concentrationsof substrate do NOTchange inhibition(noncompetitive)

22. No inhibitor Competitive Inhibitor rate Noncompetitive Inhibitor Substrate concentration Inhibitors • Inhibition

23. Enzyme inhibition - youtube http://www.youtube.com/watch?v=MwIR7-JN3T8

25. Chemical Connections page 592

26. E1 E2 E3 A B C D Product D may inhibit E1 Enzyme Regulation • Feedback Control • Regulation by environmental control • One enzyme may control the activity of another!

27. Enzyme Regulation • Proenzymes • Enzymes manufactured may need a small polypeptide removed to become active • Also called zymogens • Example: • trypsin is synthesized as trypsinogen • trypsinogen is the inactive form • once in the digestive tract it is converted to trypsin

28. Enzyme Regulation • Allosterism • regulation at site other than active site • regulatory site • active site changes and becomes more or less reactive • positive modulation • negative modulation • “regulator” • “Thus the allosteric enzyme is controlled by the regulator.”

29. Enzyme Regulation • Isoenzymes • Same enzyme, but different form, in different tissues: • Lactate dehydrogenase (4 subunits) made from two different types – H and M • H4 predominates in heart • M4 predominates in liver and skeletal muscle

30. Medical Diagnosis • Most enzymes are confined to cells • Small amount can be found in blood, urine, etc. • Analysis of body fluids can help diagnose disease or injury (enzymes spilled to serum) • E.g. Heart Attack (???) --- check serum levels: • AST aspartate aminotransferase • LD-P lactate dehydrogenase • CK creatine kinase

31. Medical Diagnosis • Enzyme Normal Fluid Disease alanine aminotransferase (ALT) 3-17 U/L serum Hepatitis acid phosphatase 2.5-12 serum Prostate cancer alkaline phosphatase (ALP) 13-38 serum Liver/bone disease amylase 19-80 serum Pancreatic disease or mumps aspartate aminotransferase (AST) 7-19 serum Heart attack or hepatitis 7-49 CSF lactate dehydrogenase (LD-P) 100-350 serum Heart attack creatine kinase (CK) 7-60 serum Heart attack phosphohexose isomerase (PHI) 15-75 serum Heart attack