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 post-translational modification, such as breaking off a piece of the molecule or adding on another molecule.
Enzyme precursors are called zymogens or proenzymes.
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.
Pro-sequences may also be involved in pro-protein transport and secretion.