The kinetics of two-substrate reactions

The kinetic analysis of two-substrate reactions is more complex due to the increased number of possible enzyme-substrate complexes. Consider the following reaction  

A large number of possible enzyme-substrate complexes may form, e.g. the binary complexes EA, EB, EP and EQ, ternary complexes EAB, EPQ, EAQ, and EBQ. Most two-substrate reactions can be grouped into two major classes, based upon the reaction sequence in the two-substrate reactions, single displacement reactions and double displacement reactions. 

In single displacement reactions both substrates A and B simultaneously must be present on the active site of the enzyme to yield a ternary complex EAB in order that the reaction may proceed. Single displacement reactions take place in two forms, random and ordered, and they are distinguished by the way the two substrates bind to the enzyme. 

In random bi-substrate reactions, either substrate may bind to the enzyme first, indicating that the ternary complex (sometimes called the central complex) EAB can be formed equally well in two different ways. 

In ordered single displacements there is a compulsory sequence for the reaction which dictates that a specific substrate, the leading substrate, must be bound first, before the second, or following substrate, can be bound, as shown below  

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