Identification of proxenin as a precursor of the peptide xenin with sequence homology to yeast and mammalian coat protein alpha.

Proxenin a precursor of the bioactive peptide xenin, was isolated from canine pancreas by HPLC and identified by mass spectrometry and sequence analysis as a pentatriacontapeptide with a molecular weight of 4035: Met Leu-Thr Lys-Phe-Glu-Thr-Lys-Ser-Ala-Arg-Val-Lys-Gly-Leu-Ser- Phe-His-Pro-Lys-Arg-Pro-Trp.Ile-Leu-Thr-Ser-Leu-His-Asn-Gly-Val-Ile-Glo- Leu-OH. Treatment with pepsin cleaved off 10 C-terminal amino acids and released xenin. Data base search showed amino acid sequence homology of xenin and proxenin with the sequence of coal protein alpha of yeast (62%) and humans (100%). Concentration of the coatomer complex from rabbit liver led to an equimolar enrichment of extractable proxenin. We conclude, therefore, that xenin and proxenin are peptide sequences highly conserved during evolution within the alpha-subunit of the coatomer.