Isomerization reaction is the process by which one molecule is transformed into another molecule that has exactly the same atoms, but the atoms are rearranged1. In some molecules and under some conditions, isomerization occurs spontaneously. Many isomers are equal or roughly equal in bond energy, and so exist in roughly equal amounts, provided that they can interconvert relatively freely, that is the energy barrier between the two isomers is not too high. When the isomerization occurs intramolecularly, it is considered a rearrangement reaction. Isomerases can lower the isomerization energy and thus increase the reaction rate.
Isomerases are sorted as EC 5 in the EC number classification of enzymes and can be further classified into seven subclasses.
The general form of isomerization reaction is as follows:
A-B → B-A
There is only one substrate yielding one product. This product has the same molecular formula as the substrate but differs in bond connectivity or spatial arrangement. Isomerases catalyze reactions across many biological processes, such as in glycolysis and carbohydrate metabolism.
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Muller P. Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)[J]. Pure and Applied Chemistry, 1994, 66(5): 1077-1184. ↩