Rmax and Km (26.4)• Constants from Michaelis-Menten equation give insight into qualitative

and quantitative aspects of enzyme kinetics– Indicate if enzyme inhibition is present and what type of inhibition is exhibited– Rmax is the maximum possible rate of conversion of substrate to product for a given

enzyme– Km is related to how tightly an enzyme binds a substrate (the higher the value, the less

tightly bound the substrate)

• Inverting the Michaelis-Menten rate law gives an equation that can be useful for obtaining the maximum rate and the Michaelis constant– Lineweaver-Burk plot is generated by plotting 1/rate vs. 1/[S]

• Lineweaver-Burk equation is more useful for getting constants since experiments can be done over a short range of substrate concentrations– y-intercept gives us Rmax, which is then used with the slope to get Km

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1rate

= KmRmax

1S[ ]

+ 1Rmax

Enzyme Inhibition (26.4)• Inhibition is a term used to describe the inability of a product being

formed due to the presence of another substance (the inhibitor)– Enzyme inhibition can be competitive or noncompetitive

• Competitive inhibition is caused when an inhibitor “competes” with the substrate in binding with the enzyme– Inhibitor decreases production of ES, thus decreasing product formation

• Noncompetitive inhibition is caused when an inhibitor can bind to either the free enzyme or the enzyme-substrate complex– Inhibitor does not allow ES complex to convert to products

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E + S k1 ⏐ → ⏐k−1

← ⏐ ⏐ ES

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E + I k I ⏐ → ⏐k− I

← ⏐ ⏐ EI

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ES k2 ⏐ → ⏐ P + E

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E + S k1 ⏐ → ⏐k−1

← ⏐ ⏐ ES

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E + I k I ⏐ → ⏐k− I

← ⏐ ⏐ EI

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ES + I k I ⏐ → ⏐k− I

← ⏐ ⏐ ESI

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ES k2 ⏐ → ⏐ P + E

Michaelis-Menten Plot for Catalyzed Reaction of CO2 with H2O

Lineweaver-Burk Plot for Catalyzed Reaction of CO2 with H2O

Enzyme Inhibition