1 / 25

380 likes | 1.17k Vues

Chapter 6.3: Enzyme Kinetics. CHEM 7784 Biochemistry Professor Bensley. CHAPTER 6.3 Enzyme Kinetics. description of enzyme kinetics by examining the Michaelis-Menten theory. Today’s Objectives : (To learn and understand the). What is (are?) Enzyme Kinetics?.

Télécharger la présentation
## Chapter 6.3: Enzyme Kinetics

**An Image/Link below is provided (as is) to download presentation**
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.
Content is provided to you AS IS for your information and personal use only.
Download presentation by click this link.
While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

**Chapter 6.3: Enzyme Kinetics**CHEM 7784 Biochemistry Professor Bensley**CHAPTER 6.3Enzyme Kinetics**• description of enzyme kinetics by examining the Michaelis-Menten theory Today’s Objectives: (To learn and understand the)**What is (are?) Enzyme Kinetics?**• Kineticsis the study of the rate at which compounds react • Rate of enzymatic reaction is affected by • Enzyme • Substrate • Effectors • Temperature**Effect of Substrate Concentration**• Ideal Rate: • Deviations due to: • Limitation of measurements • Substrate inhibition • Substrate prep contains inhibitors • Enzyme prep contains inhibitors**Plot V0 vs. [S]**• Michaelis-Menten Equation • Describes rectangular hyperbolic plot • Vo = Vmax [S] • Km + [S]**Vmax = velocity where all of the enzyme is bound to**substrate (enzyme is saturated with S) Km = [S] @ ½ Vmax (units moles/L=M) (1/2 of enzyme bound to S)**E**S k-2 Initial Velocity Assumption • Measurements made to measure initial velocity (vo). At vovery little product formed. Therefore, the rate at which E + P react to form ES is negligible and k-2 is 0. Therefore E + S E + P k1 k2 E + S ES E + P k-1**E**S k1 k2 E + S ESE + P k-1 Steady State Assumption Steady state Assumption = [ES] is constant. The rate of ES formation equals the rate of ES breakdown E + S E + P**E**S E + S k1 E + S ES Rate of ES formation Rate = k1 [E] [S]**E**E S S E + S E + P k-1 k2 ES E + S ES E + P • Rate of ES breakdown Rate = (k2 [ES]) + (k-1[ES]) Rate = [ES](k2 + k-1)**Therefore………if the rate of ES formation equals the**rate of ES breakdown 1) k1[E][S] = [ES](k-1+ k2) 2) (k-1+ k2) / k1 =[E][S] / [ES] 3) (k-1+ k2) / k1 = Km (Michaelis constant)**What does Km mean?**• Km = [S] at ½ Vmax • Km is a combination of rate constants describing the formation and breakdown of the ES complex • Km is usually a little higher than the physiological [S]**What does Km mean?**• Km represents the amount of substrate required to bind ½ of the available enzyme (binding constant of the enzyme for substrate) • Km can be used to evaluate the specificity of an enzyme for a substrate (if obeys M-M) • Small Km means tight binding; high Km means weak binding Hexokinase Glucose + ATP <-> Glucose-6-P + ADP Glucose Km = 8 X 10-6 Allose Km = 8 X 10-3 Mannose Km = 5 X 10-6**k1**kcat E + S ES E + P k-1 What does kcat mean?**Aren’t Enzymes Kinetics Fun?!**• The final form of M-M equation in the case of a single substrate is • kcat (turnover number): how many substrate molecules can one enzyme molecule convert per second • Km (Michaelis constant): an approximate measure of substrate’s affinity for enzyme**Limitations of M-M**• Some enzyme catalyzed rxns show more complex behavior E + S<->ES<->EZ<->EP<-> E + P With M-M can look only at rate limiting step • Often more than one substrate E+S1<->ES1+S2<->ES1S2<->EP1P2<-> EP2+P1<-> E+P2 Must optimize one substrate then calculate kinetic parameters for the other • Assumes k-2 = 0 • Assume steady state conditions**V max**Km Km ~ 1.3 mM Vmax ~ 0.25**1/ 1/**-1/Km = -0.8 Km = 1.23 mM 1/Vmax = 4.0 Vmax = 0.25

More Related