Friday, October 1, 2010, Lecture 16
Announcements:
1.
Quiz 4 results:
A 25.7
B 23.7
C 23.8
2.
Today at 2:55PM in Comstock B108: "Graduate school: What is expected of you,
and what are your career options after your degree?”
3. Panel discussion re treatment of infants with ambiguous sex: Hollis E. Cornell Aud,
132 Goldwin Smith, Mon. 10/4 from 5:00  6:30PM
Wednesday’s lecture:
•
Some properties of the MichaelisMenten Equation
•
How to measure Km and Vm by use of the LineweaverBurk (doublereciprocal) plot
•
The ES dissociation constant K
S
= k
1
/k
1
•
An
elementary rate constant
corresponds to one energy barrier to reach a transition
state
Today’s lecture:
Page 116, details of how to go from kinetic data to the LineweaverBurk plot:
1.
Calculate the reciprocals
.
Initially the data are in the form V
in
vs
[S].
2.
Graph the reciprocals
.
3.
Extrapolate the straight line
to reach the intercept at 1/V
in
= 0.0 on the xaxis.
For the example on page 116, you determine that 1/V
M
= 100 M
1
min.
Thus
V
M
= 0.01 M min
1
.
4.
Then, extrapolate to the xaxis to find:
1/K
M
= 200 M
1
, thus K
M
= 1/200 M
1
= 0.005 M
In summary, using the LineweaverBurk plot requires either graph paper and a straight
edge, or proper use of a calculator, or plotting and analysis using e.g. Excel.
But note
that on an exam, you will have graph paper and no access to Excel.
Page 117
Turnover number
is the number of substrate molecules converted to
product per unit time when enzyme is saturated with substrate. This corresponds to k
cat
,
V
m
= k
cat
[E]
total
Notice that k
cat
is used, not k
2
, because this rate constant might be more complex than
a simple elementary rate constant.
Turnover number (actually, its reciprocal) is the
answer to the question, “How much time passes, once substrate has bound, until the
chemical rxn is completed?”.
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View Full DocumentLook at the table at the top right of page 117.
The first enzyme, carbonic anhydrase,
has a turnover number of 6x10
5
sec
1
.
Wow, fast!
This number is the k
cat
.
Consider
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 Fall '09
 feig
 Enzyme, Enzyme inhibitor, Glu

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