# Help on Enzymes (finding max. rate)

Steve Mcclue Steven_Mcclue-1%notes at sb.com
Thu Nov 16 04:04:20 EST 1995

In article <swest-1511952031220001 at swest.anglianet.co.uk>, swest at mail.anglianet.co.uk says...
>
>   I am doing an A-level project on the rate of Urease in relation to the
>concentration of substrate. Having acheived some results, I have been told
>by my Biology teacher that there is a way of extrapolating the exact value
>for the maximum rate, by plotting a graph of 1/Rate against 1/Substrate
>concentration, and then doing something with the point where the line
>crosses the x axis. Unfortunately I don't know exactly what to do, and
>neither does my teacher (he goes off muttering about 'Michaelis Merton',
>or something). Can anybody help, or at least tell me where I can find out
>
>   Chris West

I think any Biochemistry textbook will tell you about the Michaelis-Menten equation,
which relates the initial rate, maximum rate and and substrate concentration in one
neat package. Here it is:

v = Vmax [S] / Km + [S]

where v = initial velocity
[S] = substrate concentration
Vmax = maximum velocity
Km = a constant, known as the Michaelis constant

You plot 1/v vs 1/[S], and you get a graph which is usually a straight line. Where the line
crosses the Y axis gives you the value of 1/Vmax. Where it crosses the X axis, this gives you
-1/Km, and the slope of the line gives you Km/Vmax.

When I was a lad, I didn't have to do this stuff before I went to University - now it's in the
A-level syllabus??

Steve