Characterization of the chicken telokin heterogeneity by time-of-flight mass spectrometry

Chicken gizzard telokin was purified to apparent homogeneity by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This preparation yielded upon mass spectrometry analysis seven mass peaks spanning from 15 858 to 17 100 Da. Anion exchange-high performance liquid chromatography of the purified telokin revealed a high diversity of telokin molecules. By combining protein chemistry to chromatography and mass spectrometry, the telokin heterogeneity was analyzed. Three acetylated N-termini were found, AMI, MIS, and SGR. Cyanogen bromide cleavage of telokin yielded six different C-terminal peptides corresponding to the removal of one to six C-terminal glutamyl residues from the protein sequence deduced from the cDNA. Phosphorylation of telokin was detected, thus increasing the heterogeneity of the telokin preparation. In addition, peptide sequencing has shown that telokin contained either an aspartyl or a glutamyl residue at position 27, probably resulting from chicken polymorphism.