Protein precursor

A protein precursor, also called a pro-protein or pro-peptide, is an inactive protein (or peptide) that can be turned into an active form by posttranslational modification. The name of the precursor for a protein is often prefixed by "pro". Examples include proinsulin and proopiomelanocortin.

Protein precursors are often used by an organism when the subsequent protein is potentially harmful, but needs to be available on short notice and/or in large quantities. Enzyme precursors are called zymogens or proenzymes. Examples are enzymes of the digestive tract in humans.

Some protein precursors are secreted from the cell. Many of these are synthesized with an N-terminal signal peptide that targets them for secretion. Like other proteins that contain a signal peptide, their name is prefixed by "pre". They are thus called pre-pro-proteins or pre-pro-peptides.cite book |author=Alberts, Bruce |title=Molecular biology of the cell |publisher=Garland Science |location=New York |year=2002 |pages=p760 |isbn=0-8153-3218-1 |oclc= |doi=] The signal peptide is cleaved off in the endoplasmic reticulum.

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