“…In addition, monoclonal antibodies are susceptible to chemical or enzymatic modification, particularly at sites that are exposed to the proteinliquid interface. Product heterogeneity can be caused by a number of modifications, such as C-terminal processing of lysine residues (Harris, 1995;Santora et al, 1999;Weitzhandler et al, 1998), deamidation (Di Donato et al, 1993;Hsu et al, 1998), glycation (nonenzymatic glucose addition) (Quan et al, 2008), amino acid sequence variations , and noncovalent complexes (Santora et al, 2001 Schnerman et al, 2004). These orthogonal assays include potency, identity and purity assays, which evaluate "critical quality attributes" such as size and charge heterogeneity.…”