Tsou plot

The Tsou plot is a graphical method of determining the number and nature of the functional groups on an enzyme that are necessary for its catalytic activity. Theory of Tsou's method Tsou Chen-Lu analysed the relationship between the functional groups of enzymes that are necessary for their biological activity and the loss of activity that occurs when the enzyme is treated with an irreversible inhibitor. Suppose now that there are groups on each monomeric enzyme molecule that react equally fast with the modifying agent, and of these are essential for catalytic activity. After modification of an average of groups on each molecule, the probability that any particular group has been modified is and the probability that it remains unmodified is . For the enzyme molecule to retain activity, all of its essential groups must remain unmodified, for which the probability is . The fraction of activity remaining after modification of groups per molecule must be and so