Carbon-14 has a specific activity of 62.5mCi per mmole (2.31GBq per mmole) and peptides containing one carbon-14 will be expected to have a specific activity in the range 50-60mCi per mmole. The simplest amino acid, glycine, can be prepared with one or both carbon atoms labelled with carbon-14 leading to a maximum specific activity of 100-120mCi/mmole; similarly the N-terminus of the peptide can be labelled with acetic acid at specific activity of up to 120mCi/mmole.
Where the use of glycine or acetic acid is not applicable it will be necessary to choose other amino acids for labelling. In these cases those amino acids that do not require side-chain protection should be considered first as the synthetic procedures are significantly less involved. In these instances we invite you to contact us to discuss your requirement in detail. Other amino acids can be labelled up to a maximum specific activity determined by the number of carbon atoms present. As with tritium, the specific activity can be increased by incorporating several amino acids labelled with carbon-14 and can be reduced by diluting with unlabelled material.