Isozymes are different forms of a single enzyme that perform the same or similar function. Each form has some small change that allows it to be distinguished from other forms (isozymes) of the same enzyme. The changes usually result from point mutations in the DNA that cause single amino-acid substitutions into the protein making up the enzyme. Changes that affect the charge or size of the final enzyme may alter its mobility in an electric field. Such changes often can be detected by electrophoresis, and this forms the basis for isozyme analysis.
The terms "isozyme" and "allozyme" often are used interchangeably and can be a source of great confusion. However, the terms are not identical. Isozymes that have been analyzed genetically and are known to be alleles at a single genetic locus can be called allozymes. Therefore, all allozymes are also isozymes, but not all isozymes are allozymes. Isozyme is a more general term and should be used unless the genetic basis of the different enzyme forms is known for certain.
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