Peptide Modifications

1. Biotin and FITC 
Fluorescein isothiocyanate (FITC) is an activated precursor used for fluorescein labeling. For efficient N-terminal labeling, a seven-atom aminohexanoyl spacer (NH2-CH2-CH2-CH2-CH2-CH2-COOH) is inserted between the fluorophore (fluoroscein) and the N-terminus of the peptide. 
For C-terminal labeling of biotin, a Lys residue is added to the C-terminus of the peptide. Biotin is then attached to the lysine side chain via amide bond. The positive charge of the lysine is then removed.

2. Amidation and Acetylation

If the peptide is from an internal sequence of a protein, terminal amidation (C-terminus) or acetylation (N-terminus) will remove its charge and help it imitate its natural structure (amide, CONH2). In addition, this modification makes the resulting peptide more stable towards enzymatic degradation resulting from exopeptidases.

3. Phosphorylation

Phosphopeptides can assist in the investigation of the influences of phosphorylation on peptides and protein structure and in the understanding of regulatory processes mediated by protein kinases. GenScript has successfully synthesized numerous serine-, threonine-, and tyrosine-phosphopeptides. For peptides containing one or more of these hydroxy-amino acids, selective phosphoryl.