Mass spectrometrical analysis of recombinant human growth hormone (Genotropin®) reveals amino acid substitutions in 2% of the expressed protein

Table 2 Results of electrospray LC-MS/MS and MALDI-TOF MS/MS measurements

Sequence	M calculated (Da)	M observed (Da)	delta M (Da)	Modification
EETQQK SNLELLR	1586.83	1614.74	27.91	K₇₀: di-methylation or → R *
FDTN SHN DDALLK	1488.68	1489.60	0.92	N₁₄₉ / N₁₅₂ deamidation
R LEDGSPR	928.47	900.46	-28.01	R₁₂₇→ Q or K *
LFDNAM LR	978.50	994.40	15.90	M₁₄ : oxidation
DM DKVETFLR	1252.61	1268.40	15.79	M₁₇₀: oxidation
DLEEGIQTLM GR	1360.61	1376.66	16.05	M₁₂₅: oxidation
LFDNAM LR	978.50	960.40	-18.10	M₁₄ → I
DLEEGIQTLM GR	1360.61	1342.60	-18.01	M₁₂₅ → I
DM DKVETFLR	1252.61	1234.60	-18.01	M₁₇₀ → I
L FDNAMLR	978.50	1035.40	56.90	Carbamidomethyl – N terminus

• Nearly isobaric mass differences
Sequences and mass differences of modified peptides detected in the Genotropin sample. Column 1: sequence of modified peptides following tryptic digestion of Genotropin^®; column 2: calculated monoisotopic masses of the unmodified tryptic peptides; column 3: observed monoisotopic masses; column 4: differences of calculated and observed masses; column 5: possible explanations of the mass differences.

ISSN: 1477-5956