BCH 4053General Biochemistry ISpring 2003 

Calculated data:
1/[S] M^{1} 
1/v no inhibitor min/mmol 
1/v inhibitor A min/mmol 
1/v inhibitor B min/mmol 
0.20 x 10^{4} 
0.80 
1.35 
2.08 
0.40 x 10^{4} 
1.15 
2.22 
3.03 
0.59 x 10^{4} 
1.49 
3.13 
4.00 
0.83 x 10^{4} 
1.85 
4.00 
5.00 
1.00 x 10^{4} 
2.22 
4.76 
5.88 
Calculated Results:
Plot 
K_{m } 
V_{max} 
LineweaverBurk 
4.0 x 10^{4} M 
2.2 mmol/min 
HanesWolff 
3.8 x 10^{4} M 
2.2 mmol/min 
EadieHofstee 
3.8 x 10^{4} M 
2.2 mmol/min 
Cornish Bowden 
3.7 x 10^{4} M 
2.1 mmol/min 
Inhibitor classification:
Inhibitor A Competitive (within experimental error)
Inhibitor B Pure noncompetitive (within experimental error)
Kinetic Data:
v 
[S] 
mmol/minmg 
M x 10^{4} 
1.25 
5 
0.87 
2.5 
0.67 
1.7 
0.54 
1.2 
0.45 
1 
Plot each data set as a separate line with a y intercept of v, and an x intercept of [S]. This gives the following family of straight lines, which are extended to the negative [S] quadrant:
If all of the v, [S] points fall on a rectangular hyperbola, then the lines should all cross at the same point, which would give Vm and Km. There can be errors in the data points, however, and the extent of the error (or deviation from a rectangular hyperbola) can be estimated by how much the crossing points deviate from each other. Drawing a box around the crossing points gives a feeling for the potential error in Vm and Km one can get from the data. (The Km would lie within the width of the box, the Vm would lie within its height).
In the above data, line two is clearly deviating from the other lines. We can illustrate this by calculating the y and x values for each line crossing, i.e. solve for y and x for each possible pair of equations:
Line Pair 
All Pairs 
Excluding Line 4 

x 
y 
x 
y 

1&2 
3.9 
2.2 
3.9 
2.2 
1&3 
4.0 
2.3 
4.0 
2.3 
1&4 
3.6 
2.1 

1&5 
4.0 
2.3 
4.0 
2.3 
2&3 
4.3 
2.4 
4.3 
2.4 
2&4 
3.2 
2.0 

2&5 
4.1 
2.3 
4.1 
2.3 
3&4 
2.3 
1.6 

3&5 
3.9 
2.2 
3.9 
2.2 
4&5 
Don’t cross 
Don’t cross 

Average: 
3.7 
2.1 
4.0 
2.3 
Therefore including line 4, Km is 3.7 x 10^{4} M, Vm is 2.1 m molmin^{1}mg^{1}
and excluding line 4, Km is 4.0 x 10^{4} M, Vm is 2.3 m molmin^{1}mg^{1}.
