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Lecture 24 Enzyme Kinetics 2
Biomolecules
University of Lincoln
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Enzyme Kinetics 2
● Enzyme 2 has the same KM as enzyme 1 but higher Vmax ○ Enzyme 2 has higher v0 than enzyme 1 at any substrate concentrations
● Enzyme 2 has same Vmax as enzyme 1 but lower KM ○ Enzyme 2 has higher v0 than enzyme 1 at any substrate concentrations
● Enzyme 2 has lower Vmax than enzyme 1 and lower KM ○ At low substrate concentrations v0 of enzyme 2 may be higher than enzyme 1 and opposite at high substrate concentration ○ Enzyme 2 may have lower v0 than enzyme 1 at any substrate concentrations
● Faster depletion of substrate (or appearance of product - to have a faster reaction) can be achieved by? ○ Increase Vmax ○ Decrease of KM ○ Increase of [E]
● Enzyme activity v0 decrease in time: ○ At any [S] ○ At any [E]
● Catalytic efficiency
● Equilibrium of the enzyme and substrate ● It is about how efficient the enzyme is to catalyse the reaction
● Kcat represents well the efficiency only when [ES] is high ● At low [S] concentrations, [ES] is small, so Kcat is not helpful ● Kcat/KM (units = M-1 s-1) is a better way to measure efficiency ● It reflects the rate of formation of product (Kcat) but also reflects how often substrate and enzyme come together (KM) ○ It is called catalytic efficiency
● If Kcat/KM approaches 10^8-10^9 M-1 s-1 (rate of diffusion of molecules) the enzyme are ‘diffusion limited’ ● Also called ‘perfect enzymes’ ● They perform catalysis every time a collision occurs between substrate and enzyme ○ The collision is the limiting factor because the catalytic efficiency is as efficient as the collision rate
● Lineweaver-Burk transformation ○ Double reciprocal plot: ■ Make the reciprocal of both sides of Michaelis-Menten equation
○ Uncompetitive inhibition ■ I binds to ES ■ K’i is the dissociation constant ○ Non-competitive inhibition ■ I binds to E and ES ■ S unaffected ■ K’i = Ki ○ Mixed inhibition ■ Same as non-competitive, but S is affected by I ■ K’i =/ Ki
● Competitive inhibition ○ I competes with S ○ When bound, prevents S to bind ○ I and S have similar structures ○ At high [S] the S outcompetes I ○ Higher apparent KM ○ Vmax unaffected
● Uncompetitive inhibition
○ I binds ES at site other than S ○ S is not prevented from binding ○ Apparent KM decreases (ES is eliminated and equilibrium shifted) ○ The catalytic step is prevented ○ Vmax decreases
○ I binds E or ES at site other than S ○ A variation of non-competitive inhibition where Ki≠K’i and therefore S binding and KM are affected (either way) ○ The catalytic step is prevented ○ Vmax decreases ○ Both KM and Vmax change, like in uncompetitive inhibition
● Michaelis-Menten equation and inhibitors
○ This will be explored more in detail in a workshop ○ The dissociation constants Ki and K’i of an inhibitor can be estimated using a modified Michaelis-Menten equation (see below) ○ The Lineweaver-Burk transformation is also useful to understand they type of inhibition
Lecture 24 Enzyme Kinetics 2
Module: Biomolecules
University: University of Lincoln
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- More from:BiomoleculesUniversity of Lincoln33 Documents
