ENZYMES

1. ENZYMES

2. ENZYMES • are biological catalyst • are mostly proteinaceous in nature, but RNA was an early biocatalyst • are powerful and highly specific catalysts

3. carbonic anhydrase

8. Many enzymes require co-factor for activity Apoenzyme + co-factor = holoenzyme

10. NOMENCLATURE: • Common name- e.g. trypsin, pepsin • Hybrid name- e.g. sucrase • Systematic name: EC 2.7.4.4 • example: nucleoside monophosphate kinase • ATP + NMP  ADP + NDP

12. ENZYMES accelerate reactions by facilitating the formation of the transition state

17. Active site • is the region where the substrate binds • contains residue that directly participate in making or breaking of bonds (formation of transition state) • is the region where activation energy is lowered • Common features • Active site is a three dimensional cleft • Takes up a small part of the total volume of an enzyme • Are clefts or crevice • Substrates are bound to enzymes by multiple weak interactions

20. Two models of the Active site • Lock and key • Induced-fit

23. Kinetic Properties of Enzymes Michaelis-Menten Equation

24. Factors Affecting Enzyme Activity • Temperature • pH • [S] • Presence of Inhibitors

25. TEMPERATURE • As the temperature rises, molecular motion - and hence collisions between enzyme and substrate - speed up. But as enzymes are proteins, there is an upper limit beyond which the enzyme becomes denatured and ineffective.

27. pH • The conformation of a protein is influenced by pH and as enzyme activity is crucially dependent on its conformation, its activity is likewise affected.

29. Kinetic Theory of Enzyme-Catalyzed Reaction • Effect of [E] • involves the reversible formation of an enzyme-substrate complex, which then break down to form one or more products • if [S] is constant, v is proportional to [E]

30. 2. Effect of [S] • has profound effect on the rate of enzyme-catalyzed reaction

32. At low [S], rate of reaction is 1o order, v is directly proportional to [S] At mid [S], rate of reaction is mixed order proportionality is changing At high [S], rate of reaction is zero order

34. Michaelis-Menten Equation

35. Significance of KM When V= ½ Vmax, what is [S]?

36. The KM of an enzyme is the substrate concentration at which the reaction occurs at half of the maximum rate.

39. There are limitations in the quantitative (i.e. numerical) interpretation of this type of graph, known as a Michaelis plot.  The Vmax is never really reached and therefore Vmax and hence KM values calculated from this graph are somewhat approximate. 

40. Lineweaver- Burk plot

42. The Effects of Enzyme Inhibitors • Competitive • In the presence of a competitive inhibitor, it takes a higher substrate concentration to achieve the same velocities that were reached in its absence. So while Vmax can still be reached if sufficient substrate is available, one-half Vmax requires a higher [S] than before and thus Km is larger • 2. Non-Competitive • With noncompetitive inhibition, enzyme molecules that have been bound by the inhibitor are taken out of the game so • enzyme rate (velocity) is reduced for all values of [S], including • Vmax and one-half Vmax but • Km remains unchanged because the active site of those enzyme molecules that have not been inhibited is unchanged.