MadSci Network: Biochemistry
Query:

Re: How do i calculate the rate of reaction of something

Date: Thu Apr 21 16:16:38 2005
Posted By: Alvan Hengge, Professor of Chemistry
Area of science: Biochemistry
ID: 1113409086.Bc
Message:

To learn about the pH dependency of catalysis by an enzyme, or for that matter, any chemical 
reaction, one measures the rate of reaction at a series of pH values, and then plots the data on a 
graph with the rate on the y-axis, and the pH on the x-axis.  This type of graph is called a pH-
rate profile.  The pH at which the reaction goes at the fastest rate is called the pH optimum.  

In your message you mention that you have collected some data, but you donít say what type of 
data, so Iím not sure if you have been able to measure rates and want to know how to analyze 
them, or if you are asking about how to measure the rate of reaction.  To measure the rate of a 
reaction, one measures either the appearance of a product, or the disappearance of a reactant, 
over time.  Such measurements can be made by using some method, called an assay, that is 
sensitive to the concentration of either the reactant or product that you want to monitor.  This 
can be done spectroscopically (for example, by following the increase in the absorption of light 
at a particular wavelength), or by chemically analyzing the reaction mixture at periodic time 
intervals. 

Once you have measured the rate of your catalase reaction at several different pH values, you will 
be ready to produce your pH-rate profile. Here is a web site that discusses the effect of pH on 
enzymatic activity that may help you:
 http://www.worthington-biochem.com/introBiochem/effectspH.html



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