N-Terminus
The end of a peptide or protein chain that has a free amino group (-NH2). Peptide sequences are conventionally written and read starting from the N-terminus. Many enzymes that break down peptides in the body (aminopeptidases) begin degradation from the N-terminus.
Technical Context
The N-terminus (amino terminus) is where peptide synthesis begins in biological systems (ribosomes read mRNA 5' to 3', producing proteins from N to C). In solid-phase peptide synthesis, however, construction typically proceeds from C-terminus to N-terminus. The free amino group at the N-terminus makes it susceptible to aminopeptidases — enzymes that sequentially remove amino acids from this end. N-terminal modifications such as acetylation or pyroglutamate formation are common strategies to protect therapeutic peptides from aminopeptidase degradation. DPP-4, which degrades GLP-1, cleaves at the penultimate position from the N-terminus.