Cysteine added during peptide synthesis

Cysteine-containing peptides can be conjugated to sulphydryl-reactive proteins, provided that the cysteine is not essential for the biological activity. If the peptide is devoid of Cys, this amino acid can be added N- or C-terminally during synthesis. Depending on the linker attached to the solid phase, C-terminal incorporation is not recommended to avoid possible racemization of Cys (17). 

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