Quantitation of phenylalanine substitution at the most prominent substitution site in the rhumAb C (HC T36) under different phenylalanine feeding conditions in 2 L fermentation runs.

*:The phenylalanine substitutions were quantified at peptide level in the harvested product (day 14) by adding the areas of the respective peak pair and dividing by the sum of the areas of the all three peaks, the native and the two altered peptide peaks. A quantification at the level of the intact or reduced protein was not possible due to lack of sensitivity and due to other potential isobaric modifications with a mass delta of +16 Da.