Download MBBS (Bachelor of Medicine, Bachelor of Surgery) 1st year (First Year) Biochemistry ppt lectures Topic 9 Enzyme Kinetics Notes. - biochemistry notes pdf, biochemistry mbbs 1st year notes pdf, biochemistry mbbs notes pdf, biochemistry lecture notes, paramedical biochemistry notes, medical biochemistry pdf, biochemistry lecture notes 2022 ppt, biochemistry pdf.
Enzyme Kinetics 2018
Learning Objectives
Enzyme Kinetics
Enzyme Inhibition
Drugs utilizing kinetics and inhibition and its clinical utility
Enzyme Kinetics
the quantitative measurement of the rates of enzyme-catalyzed reactions
and the systematic study of factors that affect these rates
Catalysts
Increase rate of reaction by factor of 106
Highly selective and specific
Not changed as a result of catalysis
Does not change the equilibrium constant
Enzymes Alter Only the Reaction Rate
and Not the Reaction Equilibrium
Factors affecting reaction velocity
Substrate concentration
The rate of an enzyme-catalyzed reaction increases with substrate
concentration until a maximal velocity (Vmax) is reached
Temperature
Bell shaped curve
Increase of velocity with temperature
Decrease of velocity with higher temperature
pH
Bell shaped curve
Effect of pH on the ionization of the active site
Effect of pH on enzyme denaturation
Variable pH optimum
Kinetic Order of Reaction
Sum of the molar ratios of the reactants defines the kinetic order of the
reaction
First order
Second order
Pseudofirst order reaction
Michaelis Menten Equation
Vmax
1/2Vmax
[Vo]
Km
Relationship between initial velocity and substrate concentration
[S]
Km and its importance
The Michaelis constant Km is the substrate concentration
at which Vi is half the maximal velocity (Vmax/2) attainable
at a particular concentration of the enzyme.
Unit?
Reflects the af inity of the enzyme for that substrate:
inverse relationship
Specific for enzyme substrate combination
Order of reaction
Clinical importance of Km
Hexokinase vs Glucokinase
Line-Weaver Burk plot
Double Reciprocal Graph
Linear curve
1
=
Km
+ 1
V0
Vmax [S]
Vmax
Linear form of Michaelis menten equation to
Determine Km and Vmax.
Units of Enzyme activity
Amount of substrate converted to product per unit time under standard
conditions of pH and Temperature
IUB unit: Katal (?mol/min)
SI Unit: (mol/sec)
Relative activities of Enzymes
Specific activity (Vmax/protein concentration): Impure Enzymes
Turnover number(Vmax/moles of enzyme): Homogenous Enzymes
Catalytic constant, Kcat [Vmax/No. of active sites(St)]: unit time-1
Catalytic efficiency: Kcat/Km (Carbonic anhydrase, ADA,
acetylylcholinesterase)
Two substrate Reactions(Bi Bi
Reactions)
Sequential
:
Random
Ordered
Ping Pong:
Double displacement reactions
Two substrate Reactions
Random
Ordered/Sequential
Ping Pong/Double Displacement
Enzyme Inhibition
Types of Inhibitions based on kinetics
Competitive Inhibition
Non-Competitive Inhibition
Un-Competitive inhibition
Competitive Inhibition
Binding at substrate binding site
Inhibitor similar to substrate
Km increased
Vmax same
Clinical Application/Drugs
Statin Drugs
Competitive Inhibitors of HMG CoA reductase
Sulpha Drug (Str. Analogues of PABA)
Inhibits Folic acid synthesis in Bacteria
Methanol Poisoning
Non-Competitive Inhibition
Substrate and inhibitor binds at dif erent sites
Not structural analogues
Decrease Vmax
Km same
Drugs/Toxins based on Non -
Competitive Inhibition
Ferrochelatase (Inhibition by Lead)
Acetylcholinesterase (Insecticides)
Cytochrome oxidase(Cyanide)
Uncompetitive Inhibition
Inhibitor binds to ES Complex
With Inhibitor
Both Km and Vmax decreases
1/V
1/S
Examples of Drugs showing
Uncompetitive Inhibition
Lithium (Inositol monophosphatase)
Phenylalanine(Placental ALP)
Classification based on Reversibility
Reversible
Irreversible: Chemical modification or Covalent modification
Irreversible inhibitors Poison Enzymes
Diisopropylflurophosphate (nerve gas): covalently binds
acetylcholinestrase
Aspirin(Cox)
Penicil in (bacterial transpeptidase)
Mechanism Based Inhibition
Suicide Inhibition
Contains chemical group that is transformed by catalytic machinery
Generates highly reactive group
Binds covalently to catalytically essential residues
Drugs based on Suicide Inhibition
Al opurinol (inhibits xanthine oxidase: Oxypurinol)
5 fluorouracil (inhibits thymidylate synthase: FdUMP)
Transition state Analogs & Abzymes
Transition state analog: A molecule with shape
similar to transition state
Catalytic Antibodies
Abzymes created using transition state analog
as antigens
Clinical Scenario 1
A 45-year-old man presents to emergency with bradycardia, blurred vision,
vomiting, increased and salivation. He is a farmer using OPC Spray for his field
and pipe ruptured. Type of inhibition?
(A) Competitive
(B) Noncompetitive
(C) Uncompetitive
(D) Irreversible
Clinical scenario 2
A 35 year old lady comes to OPD with evening fatigue, eyelid drooping,
dysphagia and slurred speech. A drug is administered with following effect.
What is true
In presence of drug
a. Competitive: Vmax same, km increased
b. Competitive : Vmax same, km decreased
1/V
c. Non-competitive: Vmax decreased, Km same
d. Non-competitive: Vmax decreased, Km decreased
1/S
Clinical Scenario 3
A patient wants to go to Manali for trekking. He took a medicine for mountain
sickness with following kinetics. What is the type of inhibition?
With Drug
A. Competitive
B. Noncompetitive
1/V
C. Uncompetitive
D. Allosteric
1/S
This post was last modified on 05 April 2022