Study on the quality of recombinant proteins using matrix-assisted laser desorption ionization time of flight mass spectrometry

Table 1 Mrs of non-glycoproteins measured by MALDI-TOF MS

Protein	Number of amino acids	Theoretical Mr	Measured Mr	Relative error (%)
IL-2	134a	15478	15610	2.8
GM-CSF	127	14477	15451	5.56
TNF-α	158a	17484	17517	0.18
nNOS	199a	22248	22306	0.26
IFN-α2b	166a	19378	19533	0.79
CaM fragment	95	10846	10851	0.05

^aAn additional methionine at the NH-2-terminal.

Table 2 Mrs of glycoproteins measured by MALDI-TOF MS

Protein	Number of amino acids	Measured Mr	Carbohydrate content (%)
EPO	166	28707	35.6
IFNα1	166	20465	5.2

Table 3 MALDI-TOF-MS analysis of the tryptic digests of EPO

rhEPO peptide	Position	Calculated mass value	Observed mass value	Relative error (%)
T1	1-4	439.5	440.5	0.23
T3	11-14	515.6	517.8	0.39
T4	15-20	735.9	735.5	-0.05
T5	21-45	glycopeptide
T6	46-52	927.1	928.4	0.14
T7	53	174.2
T8	54-76	2525.3	2525.5	0.01
T9	77-97	glycopeptide
T10	98-103	601.7	600.8	-0.15
T11	104-110	802.5	803.4	0.11
T12	111-116	586.3	585.5	-0.14
T13	117-131	glycopeptide
T14	132-139	923.0	923.5	0.05
T15	140	146.2
T16	141-143	434.5	*
T17	144-150	898.0	899.1	0.12
T18	151-152	203.2
T19	153-154	259.3
T21	163-166	447.4	*
T2-S-S-T20	1615.8	1612.7		-0.19

*A wide unresolved peak caused by T₁, T₁₆ and T₂₁.