Transcript Chapter 14 Part 1

Chapter 7
Chem 341
Suroviec Fall 2013
I. Introduction
•
The structure and mechanism can reveal quite a bit about an enzyme’s function
A. Reaction Kinetics
SP
Progress of this reaction can be expressed as a velocity
A. Reaction Kinetics
•
When enzyme concentration is help constant the reaction velocity
will vary with [A]
II. Michaelis – Menton Eqn.
A.
Rate equations describe chemical
processes
•
Unimolecular reactions
•
Bimolecular reactions
B. Michaelis Menton Equation is rate equation
•
Simplest cases enzyme binds to substrate before converting to product
•
The reaction of E + P converting back to ES is a step that we assume does
NOT happen.
B. Michaelis Menton Equation
•
•
We can measure n by choosing the experimental conditions
We then further choose experimental conditions to simplify the calculations:
STEADY STATE
C. Michaelis Constant (Km) and Initial Velocity (n) and Maximal Velocity (Vmax)
C. Michaelis Constant (Km) and Initial Velocity (n) and Maximal Velocity (Vmax)
•
•
•
•
Occurs a high substrate concentration when enzyme is saturated
At substrate concentration at which [S] = KM
So if enzyme has small Km achieves max catalytic efficiency at low [S]
KM is unique for each enzyme- substrate pair
C. Michaelis Constant (Km) and Initial Velocity (n) and Maximal Velocity (Vmax)
•
Michaelis Constant is a combination of 3 rate constants that is experimentally
determined.
D. kcat catalytic constant = turnover #
•
How fast an enzyme operates after it has selected and bound its substrate.
•
Number of catalytic cycles that each active site undergoes per unit time
E. kcat/KM = measure of efficiency
•
Enzyme effectiveness depends on ability to bind substrates and rapidly convert
F. Analysis: Find Vmax , KM
•
•
High values of [S] lead to vo asymptotically reaching Vmax
Use linear plot
– Lineweaver-Burk
G. Exceptions to M-M Model
1. Multi-substrate reaction
G. Exceptions to M-M Model
2. Multi-step reactions
3. Non-hyperbolic reaction
II. Inhibition
•
Substance that reduces an enzyme’s activity by influencing
– Binding of substrate
– Turnover number
•
Variety of mechanisms
– Irreversible enzyme inhibitors
• Inactivators
– Reversible
• Diminish enzyme’s activity by interacting reversibly
• Structurally resemble substrates
• Affect catalytic activity without interfering with substrate binding
A. Competitive Inhibition
•
Compete directly with normal substrate for binding site
•
Resemble substrate
•
Specifically binds to active site
•
Product inhibition
A. Competitive Inhibition
•
Transition state analogs
•
Depends on inhibitor binding selectively with RAPID equilibrium
A. Competitive Inhibition
•
M-M equation for competitive
inhibition reaction
1. KI can be measured
B. Transition State Inhibitors
•
•
Inhibitor binds to ES complex
Not to free enzyme
C. Mixed Inhibition
•
Interact in a way with the enzyme that affects substrate binding
III. Allosteric Regulation
•
1.
2.
Organism must be able to regulate catalytic activities
–
Metabolic processes
–
Respond to changes in environment
Control of enzyme availability
•
Amount of given enzyme in a cell depends on its rate of synthesis and its
rate of degradation
Control of enzyme activity
•
Catalytic activity controlled through structural alteration
•
Can cause large changes in enzymatic activity