Peptides with only one cysteine in their sequence allow chemical conjugation to other biomolecules as a single point attachment. However, the preferred conjugation points are the peptide's N-terminal C-terminal end. A cysteine placed at either end will keep the COOH free (non-conjugated) as in a native peptide or protein. For peptides that need to have a free N-terminus, add the cysteine to the C-terminus of the peptide. For internal peptides, place the cysteine can at either end. However, it is easier to synthesize peptides containing an N-terminal cysteine. Cysteine also allows the coupling of peptides to Sepharose beads useful for affinity purification of antibodies. Avoid amino- or carboxyl-conjugation chemistries since most peptides contain several amino and carboxyl groups available within the peptide sequence resulting in multi-point attachment and peptide distortion.