3.2 Basic Kinetics

Chemical Reaction Equation 1:

A --> B
The rate equation for a first order reaction, such as this one, is:

(k1 is negative because A is disappearing)

Chemical Reaction Equation 2:

A + B --> C
The rate equation for a second order reaction such as this one is:

An enzymatic reaction:

The symbols represent (in our example):
E enzyme (b-galactosidase)
S substrate (lactose)
ES enzyme-substrate complex
P product (glucose or galactose)

First consider the initial velocity of the reaction. In this case, there will be a negligibly small amount of product present ( [P]<5% of [S] is considered negligible). Under these conditions, the back reaction is negligible, that is, k-2[P]= 0 (approximately). The initial velocity is simply:

			Vo = k2[ES]		(1)

The problem with this equation is that the quantity [ES] cannot be measured. However,
[S] (the initial concentration of substrate) is known,
[P] (product produced) can be measured, and
[E]tot (the amount of enzyme added to the reaction) is known.

Now what we can do is use the rate equations plus a few other assumptions to derive an expression for [ES] (which we cannot measure) in terms of quantities which we can measure ([S], [P], and [E]tot). Okay, here we go . . .

shanec@mit.edu