The Duplex by Glenn McCoy
Read 17.1, 17.2, 17.4
Solutions to PS #2 are posted online.
A sample exam is also posted. Give it a try under
simulated conditions: 45 min, closed book, etc.
Solutions will be posted on Friday. 1 2
Rate = k [ES]
Enzyme mechanism 2
Enzyme highly specific catalyst Can’t measure [ES]
See Silberberg 16.26 k 1E][S] k–1ES] + k [2S] (steady state approx)
[ES] = k–1 k 2
So the rate is
Rate = k 2 k + k
E = free enzyme You are expected to know how to arrive at this result.
S = substrate
The next page shows how to obtain the final result.
ES = enzyme–substrate complex
You are not responsible for the derivation but you
Step 1 E + S ES should know the page after that (p. 5) on how to use
the final equation and the plot on p. 6.
Step 2 ES E + Products
Or on one line E + S ES E + Products
Unfortunately, it is not convenient to measure the k + k
Define K =M –1 2
concentration of the free enzyme. k 1
K M Michaelis – Menten constant
Instead, the total enzyme concentration [Eo] is
measured. (it includes the free and bound enzyme). k2[Eo][S]
Rate = K + [S]
[Eo] = [E] + [ES]
So [E] = [Eo] – [ES]
2 extreme case:
And[E= S] k1[E][S]
k–1+ k2 1. [S] >> K M
(k + k ) [ES] = k [E ][S] – k [ES][S] k2[Eo][S] st
–1 2 1 o 1 Rate [S] = k 2E o 1 order ?
(k–1 k 2 [ES] + k 1ES][S] = k 1E ]oS]
But [E o] = constant pseudo zero order!
[ES] = 2. [S] << K
k–1 k +2k [S1 M
k1 2[E o[S] k2[Eo][S] k2 st
Rate = k2 [ES] = k + k + k [S] Rate K M = K M [Eo][S] pseudo 1 order!
–1 2 1 5 6
A catalyst is a substance that increases the rate of rxn
without being consumed.
Catalysts occur in all parts of nature, the environment
and chemical industry.
The human body functions because of enzymes
(which are really catalysts).
How does the catalyst do it?
It provides an alternative path with a lower activation
energy for both the forward and reverse rxns.
It allows equilibrium to be rea