In addition these new derivatives have both reduced the cost of the phospho-peptide and increased the overall yield returned to investigators. Currently the PDTC is regularly synthesizing peptides with phosphorylated forms of serine, threonine, and tyrosine. These peptides can be as long as 20 amino acids, although at this length yields begin to drop dramatically. Peptides with more than one phosphorylated residue can be manufactured. Recovery amounts vary dramatically depending on the particular sequence of each peptide.
Special pricing is available for the non-phosphorylated form of the peptide for use as a control.
The largest factor appears to be steric hinderance during the phosphorylation reaction. Surrounding the phosphorylation site with residues such as histidine, arginine, cysteine, etc., can cause problems. Yields drop dramatically when the phosphorylation site is more than eight residues from the amino terminus of the peptide. The amino terminus should be a less bulky and uncharged amino acid such as glycine. Constant innovations in chemistries and protocols are allowing us to synthesize longer and more complex phospho-peptides.