### Enzyme Kinetics: Answer Sheet Example

Example Problem:
You are given a 4.0 mg/ml solution of an enzyme (Mr = 40,000 Da).
You determine initial velocities (vo) at several concentrations of substrate, [A].
a) Determine Km and Vmax.
b) Calculate kcat for the reaction.
c) Submit your calculations and a graph of 1/vo vs. 1/[A].
What we know from the problem:
1) Concentration of the enzyme = 4.0 mg/ml.
2) Enzyme Mr = 40,000 Da
What we found in the experiment:
[A]
(mM)
vo
(mM/min)
1/[A]
(mM-1)
1/vo
(min/mM)
```  0.25
0.4
0.7
1.0
2.0
3.0
5.0
8.0
12
20
```
```0.060
0.080
0.130
0.160
0.250
0.310
0.360
0.390
0.430
0.460
```
```4.00
2.50
1.43
1.00
0.50
0.33
0.20
0.13
0.08
0.05
```
```16.67
12.50
7.69
6.25
4.00
3.23
2.78
2.56
2.33
2.17
```
The enzyme concentration = (4 mg/l)/(40,000 g/mol) = 0.10mM (10-7 M).
The last two columns were calculated using equations from the Enzyme Kinetics page.

Graph of the calculated results: The Km = 2.0 mM; Vmax = 0.5 mM/min.
The kcat = Vmax/[enzyme] = (0.5 mM/min)/(0.10mM) = 5¥103 min-1. MM.xls is the Excel spreadsheet used to calculate and graph these results; it can be copied to your disk.

8.20.03