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 fro m canine pancreas by HPLC and identified by mass spectrometry and sequ ence analysis as a pentatriacontapeptide with a molecular weight of 40 35: le-Leu-Thr-Ser-Leu-His-Asn-Gly-Val-Ile-Gln-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 coat protein a of yeast (62%) and humans (100%). Concentration of the coatomer complex from rabbit liver led to an equi molar enrichment of extractable proxenin. We conclude, therefore, that xenin and proxenin are peptide sequences highly conserved during evol ution within the ru-subunit of the coatomer.