Isoelectric point

Isoelectric point (pronunciation: /ˌaɪsoʊɪˈlɛktrɪk ˈpɔɪnt/), often abbreviated as pI, is a term used in Biochemistry and Molecular Biology to describe the pH at which a particular molecule or surface carries no net electrical charge.

Etymology

The term "isoelectric" comes from the Greek words "isos" meaning equal, and "electric" meaning pertaining to electricity. The "point" refers to the specific pH at which the molecule is electrically neutral.

Definition

The isoelectric point is the pH at which a particular molecule carries no net electrical charge or the pH at which the molecule is electrically neutral in the statistical mean. The concept is often used in the study of Proteins, where it is used to analyze protein solubility in relation to pH and used in various methods of protein purification.

Calculation

The calculation of the isoelectric point of a protein or a peptide is based on the pKa values of its amino acids. The pI value is very important in the Electrophoresis technique, as it can be used to determine the direction of migration for a particular protein.

Related Terms

• pH
• pKa
• Amino Acids
• Proteins
• Electrophoresis
• Biochemistry
• Molecular Biology

See Also

• Acid dissociation constant
• Zwitterion

External links

• Medical encyclopedia article on Isoelectric point
• Wikipedia's article - Isoelectric point

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