Massspectrometrical analysis of recombinant human growth hormone Norditropin® reveals amino acid exchange at M14_V14 rhGH

Recombinant human growth hormone (rhGH) is used for the treatment of several disorders. Structural integrity of rhGH is of critical importance for its clinical use and modifications thereof may act as markers in situations such as rhGH doping, as illegal rhGH-abuse in sports is of increasing interest. In the current study we investigated homogeneity of Norditropin (R), a recombinant human growth hormone frequently used in medicine, expressed in E. coli, strain MC1061. The most recent proteomics technologies including 2-DE, MALDI-MS followed by MALDI-MS/MS and LC-MS followed by LC-MS/MS were used for the characterisation of rhGH. MALDI-TOF-TOF and electrospray LC-MS analysis revealed one major protein with an average molecular mass of 22 126.0 Da and some additional minor components. Electrospray LC-MS/MS of the enzymatically digested Norditropin (R) sample showed deamidation of N12N149 and N-159, oxidation of M-14, M-125 and M-170 and one amino acid exchange V-14 for M-14 present in < 1% of Norditropin (R). While deamidation and oxidation may be due to technical reasons, the single amino acid exchange may reflect infidelity of translation rather than codon usage and copy editing by E. coli.