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. A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Peptides (from the Greek πεπτος, digestible), are the family of short molecules formed from the linking, in a defined order, of various α-amino acids. ... Posttranslational modification is the chemical modification of a protein after its translation. ... It has been suggested that Oral insulin be merged into this article or section. ...

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. A zymogen or a proenzyme, is an inactive enzyme precursor. ... A proenzyme is the inactive precursor to an active enzyme. ...