Properties of Enzymes

1. Properties of Enzymes

2. Enzymes are catalystsWhat properties wouldideal catalysts have?

3. Enzymes are catalystsWhat properties wouldideal catalysts have? • High degree of specificity for their substrates. • Accelerate chemical reactions tremendously. • Function in mild conditions. • Be recycled to participate again.

4. A Few Definitions Cofactor – additional chemical component needed for catalysis. - often an inorganic metal ion (mineral). Coenzyme – complex organic molecule needed for catalysis. - often a vitamin. Prosthetic group – non amino acid portion of the enzyme needed for catalysis. Often a coenzyme or metal ion. Holoenzyme – complete catalytically active enzyme, with all necessary prosthetic groups. Apoenzyme – The protein part of the holoenzyme. Prosthetic groups are absent.

5. Six Classes of Enzymes • Oxidoreductases • Transferases • Hydrolases • Lyases • Isomerases • Ligases

7. Stored electrons One bond to oxygen Two bonds to oxygen

9. Amino group transferred

11. Water did chemistry to break a bond

13. CO2 was removed

14. 5.

15. 5. Amino group switched places

16. 6.

17. 6. Two substrates were ligated together

18. Enzyme Kinetics E = enzyme S = substrate P = product ES = enzyme-substrate complex k = rate constant

19. The rate of reaction is dependent on enzyme concentration [Enzyme] <<< [substrate] Figure 5.2 Velocity, or how fast the reaction is going Concentration of enzyme

20. When measuring ratesof enzyme-catalyzedreactions, initialvelocity (vo) is measured. Figure 5.3

21. Enzyme kinetics terminology [S] – substrate concentration Vo – initial velocity of a reaction. A significant amount of substrate has not yet been converted to product. Vmax – maximal velocity of a reaction. Addition of more substrate will not increase the rate of the reaction. Km – The concentration of substrate at which the rate of the reaction is half-maximal

22. Michaelis-Menten equation Page 141

23. The rate of reaction is dependent on substrate concentration Figure 5.4

24. Km values are often just above the substrate concentrationin a cell. Rates of reaction are sensitive to small changesin cellular substrate concentrations.

25. kcat is a measure of the number of substrate moleculesconverted to product per second per enzyme molecule

27. Experimental determination of kinetic constants Figure 5.6

28. Reversible Enzyme Inhibition An inhibitor is a compound that binds to an enzyme andinterferes with its activity. Many drugs are enzyme inhibitors. An inhibitor is characterized by an inhibition constant (Ki).

30. No Inhibitor Figures 5.8 and 5.9

33. No Inhibitor

36. Many competitive inhibitorsare substrate analogs Benzamidine is an inhibitor of the enzyme trypsin

37. Many competitive inhibitors are substrate analogs. Compound (b) designed as an inhibitor of the enzymepurine nucleoside phosphorylase, that utilizes guanosine (a) asa substrate. (b) is a possible drug for the treatment of arthritis. Figure 5.13

38. Irreversible Enzyme Inhibition Some inhibitors are compounds that form a stable covalentbond with the target enzyme. DFP inactivates serine proteasesby covalently modifying anactive site serine residue. Figure 5.15 F-

39. Regulation of enzyme activity by metabolite concentration Activator

40. Regulator ADP binds at an allosteric site, Separate from the active site

41. The activity of the some enzymes isregulated by reversible phosphorylation. Example: pyruvate dehydrogenase Figure 5.22