Table S2.

The ratio of protein-conjugated maleimide to total maleimide in 10% heat-inactivated fetal bovine serum (FBS) and 0.9 mg/mL bovine serum albumin (BSA)

Medium	Ratio of maleimide conjugation
10% FBS	52.6%±1.3%
0.9 mg/mL BSA	69.2%±0.6%

Note: Data are expressed as the mean ± standard deviation; n=3.