Endogenous and Exogenous
Definition
Endogenous describes a molecule the organism makes itself, such as native GLP-1 or growth hormone. Exogenous describes one introduced from outside. The distinction matters in assay work, because an exogenous analogue and the endogenous hormone it mimics can both be present in a sample.
Terms used in this definition
Other entries this definition refers to.
What this means for research sourcing
Foundational terminology for researchers new to peptide science. Volta's beginner resources connect these fundamentals to the compounds available for study.
Related Terms in Basics
Recombinant
Produced by an engineered organism rather than by chemical synthesis. A gene is expressed in bacterial or mammalian cells and the product is purified from the culture. Longer chains such as somatropin are made this way; short peptides are usually synthesised instead.
Bioregulator
A very short peptide, typically two to four residues, from a line of work begun in Russia by Khavinson and colleagues and based on fragments reported in specific tissues. The published evidence is largely Russian-language and the group has little independent replication.
Neuropeptide
A peptide that neurons release to signal to one another, acting as a transmitter or as a modulator of other transmitters. Semax and Selank are the examples most often cited in this class, both registered in Russia.
Signaling Peptide
A peptide whose function is to carry a message, binding a receptor to change what a cell does. Appetite, fluid balance and pituitary output are all regulated this way, by GLP-1, oxytocin and kisspeptin respectively.
D-Retro-Inverso
A design in which the sequence is read backwards and every L-amino acid is swapped for its D isomer. Side-chain geometry comes out close to the original while proteases, which recognise L-residues, no longer cut it. FOXO4-DRI is built this way.
Cyclization
Closing a peptide into a ring, head to tail or through a side-chain bridge. The ring has fewer conformations to lose and no free ends for exopeptidases to attack, which is why so many peptide drugs are cyclic.
PEGylation
Attaching polyethylene glycol chains to a peptide. The added hydrodynamic bulk slows glomerular filtration and shields the backbone from enzymes, so the molecule circulates for longer. PEG-MGF carries the name of the modification.
Acylation
Attaching a fatty acid chain so the molecule binds reversibly to serum albumin. The albumin-bound fraction acts as a circulating reservoir and clearance slows from hours to days. Semaglutide and cagrilintide both use it.