Glossary
Linear Peptide
A linear peptide is an unbranched chain with free N- and C-termini and no ring. Why most research peptides are linear, and the price they pay for it.
Linear peptides are unbranched amino acid chains held together by peptide bonds, with an unmodified N-terminus at one end, an unmodified C-terminus at the other, and no covalent bond closing them into a ring. Most research peptides belong here — BPC-157, ipamorelin, the GHRH analogs and the incretin family among them.
Advantages and drawbacks of a linear chain
The benefits are practical ones. Solid-phase synthesis produces linear sequences directly, without an extra cyclisation step, which means better yields and a lower price per milligram; analysis is also easier, since mass and retention time between them mostly confirm identity without any questions about connectivity.
The downside is vulnerability. Open ends are attacked by aminopeptidases and carboxypeptidases, and a flexible chain explores many shapes, so its intrinsic affinity is frequently below that of a constrained counterpart. For that reason linear peptides are more often where modification begins than where it ends: acetylating the N-terminus and amidating the C-terminus block the ends, while PEGylation and DAC slow down clearance. Contrast with the cyclic peptide entry; see how sequences are written.
Related terms
native sequence · analog