Tritiated peptides. Part 101. Catalytic exchange labelling of β-corticotrophin- (1-24) -tetracosapeptide

β‐Corticotrophin‐ (1‐24) ‐tetracosapeptide β‐Corticotrophin‐(1‐24)‐tetracosapeptide: tetracosactrin, Synacthen® (trade name of CIBA‐GEIGY Basle) Ser‐Tyr‐Ser‐Met‐Glu‐His‐Phe‐Arg‐Trp‐Gly‐Lys‐Pro‐Val‐Gly‐Lys‐Lys‐Arg‐Arg‐Pro‐Val‐Lys‐Val‐Tyr‐Pro. was labelled to a level of 0.48 Ci mmol−1 by catalytic exchange of a protected synthetic precursor with tritium gas. Over 80% of the isotope was incorporated into acid‐stable sites in the histidine residue. Smaller amounts were incorporated into methionine (5%), tyrosine (3%), phenylalanine (5%) and tryptophan (2%). Aminobutyric acid was formed (1%) by degradation of methionine and had incorporated tritium (5%). The labelled amino acid residues were stereochemically pure within the limits of experimental error.