Through optimized PEGylation reaction, a high total PEGylation ratio can be obtained (about 60%-70%). The gradient SDS-PAGE monitoring (Figure 4) showed that the un-PEGylated counterparts from the reaction mixture were successfully removed by Sephacryl S-100 chromatography or Superdex 75 chromatography. In the MALDI-TOF-MS analysis ( Figure 5 ), one-mer, two-mer, and three-mer PEGylated isomers with 49899.4 Da, 70430.9 Da, and 91057.6 Da (the molar ratios of 1:1, 2:1, and 3:1 of (mPEG) 2 -Lys-NHS:α-MMC) were detected from α-MMC-PEG conjugates.