Western blots of Aer-Cys proteins showing examples of low (Aer-V246C), intermediate (Aer-L220C), and high (Aer-S265C) PEGylation under native (N) conditions. PEGylated Aer (Aer-PEG) has an apparent mass increase of ~10 kDa. Samples denatured (D) without β-mercaptoethanol quencher were PEGylated to apparent completion; samples pretreated with β-mercaptoethanol (before PEG-mal) were not PEGylated (see Aer-V260C, βMe lane). Faint bands migrating faster than an Aer monomer represent PEGylated Aer break-down product (Ma et al., 2004). Abbreviations: D, denatured; N, native; β-Me, β-mercaptoethanol.