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6
Enzymes
6
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2, 6
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4, 6
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[PNPP]
What do we get?

What is enzyme kinetics?
• Kinetics is the study of the rate at which
compounds react
• Rate of enzymatic reaction is affected by:
– enzyme
– substrate
– effectors
– temperature

Rate Enhancement by Enzymes

Why study enzyme kinetics?
• Quantitative description of biocatalysis
• Determine the order of binding of
substrates
• Elucidate acid-base catalysis
• Understand catalytic mechanism
• Find effective inhibitors
• Understand regulation of activity

How to Do Kinetic Measurements
Experiment:
1) Mix enzyme + substrate
2) Record rate of substrate disappearance/product formation as a function
of time (the velocity of reaction)
3) Plot initial velocity versus substrate concentration
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(in which [ES] turns out to be abs
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youtube
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Vmax?

V0

[S]
Two solutions
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2) Is there an alternative method for viewing a rectangular
hyperbola that allows both Km and Vmax to be read easily? Of
course
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...
youtube
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It is the number of
substrate molecules that a single enzyme molecule converts to
product per second
...

So how does the turnover number fit in?

Enzyme kinetics – useful
parameter #2
Specificity constant, kcat/Km

This is a ratio that allows different enzymes to be compared for
catalytic ‘perfection’
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kcat /[Km]

So how does the turnover number fit in?

Enzyme efficiency is limited by
diffusion: kcat/KM
• Can gain efficiency by having high velocity or
affinity for substrate
– Catalase vs

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