How to work out Vmax / Km

Question

from a lineweaver burk plot, I have calculated slopes of 12.42 and 1.38.

 

The y intercept is 1.493 and 1.031 w/ respect to the slopes.

 

Please include working out if possible thanks 

Answer 1

The y-intercept represents 1/V_max.  So, if you have y-intercepts of 1.493 and 1.031, then the corresponding V_max values will be 0.6698 and 0.9699, respectively.  I assume one is control, and one is with inhibitor or activator?

 

The slope of the LB plot represents K_m/V_max.  Again, for the two situations you present, you will have:

K_m/0.6698 = 1.493 and K_m/0.9669 = 1.031.  Solving for K_m, you obtain 1.00 and 0.997 (units unknown as they aren't included in the question).  You will note that the K_m has not changed, so if this is an inhibitor study, then it would be non-competitive.

 

Final note:  It is easier to obtain the Km from the x-intercept, where that intercept represents -1/K_m.