Protein precursor

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A protein precursor 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 or prepro, for example, proinsulin being the precursor for insulin.

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. Enyzme precursors are called zymogens or proenzymes. Examples are enzymes of the digestive tract in humans.