Erratum to: Sequence Elucidation of an Unknown Cyclic Peptide of High Doping Potential by ETD and CID Tandem Mass Spectrometry

Erratum to: J. Am. Soc. Mass Spectrom (2011) 22:718-730

DOI: 10.1007/s13361-011-0080-5

The sequence of the unknown peptide proposed in our published article is now found to be incorrect, though at the time of publication it was the reasonable and best candidate to the unknown peptide based on all the experimental data obtained. Recently, Dr. Rohan Steel (Racing Analytical Services Ltd, Flemington, Victoria, Australia) established that the peptide was 2′,6′-dimethyltyrosine-D-Arg-Phe-Lys-NH2 ([dmt¹]DALDA), with an elemental composition of C₃₂H₅₀N₉O₅. Dr. Rohan Steel initially compared and found agreement between the theoretical m/z values for the multiply protonated species of [dmt¹]DALDA and its predicted CID product ions and experimental m/z values for the unknown peptide and its product ions. He then communicated this finding to us. We did the same comparison and found the agreement too. Additionally, we compared the theoretical and experimental m/z values for the c- and z-product ions from ETD, and they are in agreement (see Table 1). Furthermore, [dmt¹]DALDA is reported to be a potent analgesic agent, and it is in accordance with the intelligence gathered on the unknown sample. Thus, we conclude that the unknown peptide is [dmt¹]DALDA. This peptide has a C-terminal amidation, and this amidation can be hydrolyzed by trypsin, which is in agreement with the experimental results.

Table 1 Comparison between theoretical m/z values for [dmt¹]DALDA, its de-amidated form and their predicted product ions and experimental m/z values for the unknown peptide, its tryptic digest and their product ions*