Isoenzyme

Isoenzymes (or isozymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction. These enzymes usually display different kinetic parameters, or different regulatory properties. The existence of isoenzymes permits the fine-tuning of metabolism to meet the particular needs of a given tissue or developmental stage. In biochemistry, isoenzymes are a type of homologous sequence that have similar functions and are found in different species.

Structure and Function

Isoenzymes are usually the result of gene duplication, but can also arise from polyploidisation or hybridisation. In contrast to allozymes, isoenzymes are multiple forms of an enzyme that are coded by different genes and may display different characteristics. They can occur in different organs or cells of the same species, or in different species that are very closely related.

Clinical Significance

Isoenzymes are of clinical importance because they can be used as biomarkers to diagnose various diseases. For example, the isoenzyme creatine kinase (CK) is often measured in blood tests as a marker of damage such as in myocardial infarction (heart attack). In this context, CK-MB is normally used as a cardiac marker to assist in diagnosing myocardial infarction.

Examples

Some of the well-known isoenzymes include Hexokinase, Lactate dehydrogenase, Creatine kinase, and Alkaline phosphatase.

See Also

• Enzyme
• Gene duplication
• Allozyme
• Myocardial infarction

References

Isoenzyme Resources
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