Neuropeptides Labeled With S-35

Methionine and cysteine containing peptides can be labelled with S-35 by coupling of S-35-cysteine or S-35-methionine with a large excess of suitably protected peptide precursors. This is illustrated for [pGlu4, Cyt6]AVP-(4-9), beta-endorphin-(5-17) and the ACTH-fragment-analogue Org 2766. Using HPLC as final purification the peptides are obtained in radiochemical yields of about 5% and radiochemical purities between 90-97%. However the specific activities obtained are much lower than the specific activities of the starting S-35-amino acids.