Structure of recombinant human interleukin 5 produced by Chinese hamster ovary cells. 
The complete peptide map of purified recombinant human interleukin 5 (rhIL-5) was determined to verify its primary structure, glycosylation sites, and disulfide bonding structure.  Each peptide fragment generated by Achromobacter protease I (API) digestion was purified and characterized by amino acid analysis and amino acid sequence analysis.  After digestion with API, we could identify all the peptides which were expected from human IL-5 cDNA sequence.  The analyses of sulfhydryl content in rhIL-5 molecule and disulfide-containing peptide obtained from API digestion indicated that active form of rhIL-5 existed as an antiparallel dimer linked by two pairs of Cys-44 and Cys-86.  In addition, we concluded that Thr-3 and Asn-28 were glycosylated.  The results indicate that primary structure of rhIL-5 is highly homogeneous and observed heterogeneity is due to the difference in the content of carbohydrate. 