Xenin: the oldest after insulin?

Xenin is a regulatory peptide first isolated from the human gastric mucosa. Using an open-access protein database MEDLINE (33 million molecules; 11 billion amino acid residues) and our original computer program, we conducted a search for the xenin motifs in the primary structure of proteins across almost the entire taxonomic range of evolution. Motifs with 40% homology to human xenin are already present in prokaryotes. Homology reaches 84-96% in single-cell algae and plants, becoming complete since bony fishes. We suppose that this regulatory peptide is more ancient and significant than is usually thought.

Biogenic Amines in Insect Antennae.

Insect antenna is a multisensory organ, each modality of which can be modulated by biogenic amines. Octopamine (OA) and its metabolic precursor tyramine (TA) affect activity of antennal olfactory receptor neurons. There is some evidence that dopamine (DA) modulates gustatory neurons. Serotonin can serve as a neurotransmitter in some afferent mechanosensory neurons and both as a neurotransmitter and neurohormone in efferent fibers targeted at the antennal vessel and mechanosensory organs. As a neurohormone, serotonin affects the generation of the transepithelial potential by sensillar accessory cells. Other possible targets of biogenic amines in insect antennae are hygro- and thermosensory neurons and epithelial cells. We suggest that the insect antenna is partially autonomous in the sense that biologically active substances entering its hemolymph may exert their effects and be cleared from this compartment without affecting other body parts.