These are forms normally associated with the loss of C-terminal lysine of the heavy chain which is caused by basic carboxypeptidases present in the cell culture.
In the case of Racotumomab-ST10L, a shift towards acidic isoforms was observed in the Mab,
which was also observed in isoelectric focusing. The increase in the acidity of a protein may be related to the presence of oxidized species, an increase of sialylated structures or different processing of the C-terminal Lys.