Tilvi Supriya, Devi Prabha, Majik Mahesh S
1 Bio-Organic Chemistry Laboratory, Chemical Oceanography Division, CSIR-National Institute of Oceanography, Dona Paula, Goa, India.
2 Department of Chemistry, Goa University, Taleigao-Plateau, Goa, India.
Eur J Mass Spectrom (Chichester). 2017 Jun;23(3):92-97. doi: 10.1177/1469066717699218. Epub 2017 Mar 30.
Butanol fraction of sacoglossan Elysia grandifolia was investigated for identifying peptides using electrospray ionisation-tandem mass spectrometry (ESI-MS/MS). Without prior isolation, the structural determination is achieved on the basis of mass fragmentation pattern and comparison with the previously established data. The ESI-MS of the fraction in the positive ion mode gave clusters of singly and doubly charged molecular ion peaks. The ESI-MS spectrum showed peaks for the presence of the peptides kahalalides F, G, R and S reported earlier. In addition, it also showed molecular ion peaks at m/z 1557.8 [M+H] and doubly charged ions at m/z 779.4 [M+2H], 790.4 [M+Na] and 796.4 [M+K]. The MS/MS at m/z 779.4 [M+2H] at collision energy 40 V obtained series of b and y fragment ions. The MS/MS spectrum showed identical fragment ion y at m/z 643 which revealed that cyclic part is identical with kahalalide F, R and S. Careful examination of the fragment ions b to b with their corresponding y fragment ions y to y, respectively and by comparison of MS/MS pattern of kahalalide S, established that proline can be replaced by tyrosine amino acid residue. The mass difference between b ( m/z 511) and b ( m/z 674) is equal to 163 which is equivalent to mass residue of tyrosine. Their y fragment ions also quickly helped in fixing the puzzle. This resulted in the identification of the peptide sequence cyclo-[Val-(5-MeHex-Val-Thr-Val-Val-Tyr-Lys-Ile)Thr-Ile-Val-Phe-Dhb)] for the new cyclodepsipeptide, kahalalide Z. Thus, ESI-MS/MS has set a trend in quick identification of new marine molecules.
利用电喷雾电离串联质谱法（ESI-MS/MS）对叶海蛞蝓（Elysia grandifolia）的丁醇馏分进行了研究，以鉴定其中的肽。无需事先分离，即可根据质量碎片模式并与先前建立的数据进行比较来完成结构测定。该馏分在正离子模式下的ESI-MS给出了单电荷和双电荷分子离子峰簇。ESI-MS谱图显示了先前报道的肽kahalalides F、G、R和S存在的峰。此外，它还显示了质荷比为1557.8 [M+H]的分子离子峰以及质荷比为779.4 [M+2H]、790.4 [M+Na]和796.4 [M+K]的双电荷离子峰。在40 V碰撞能量下对质荷比为779.4 [M+2H]进行MS/MS分析，得到了一系列b和y碎片离子。MS/MS谱图显示质荷比为643处有相同的碎片离子y，这表明其环状部分与kahalalide F、R和S相同。通过分别仔细检查b到b的碎片离子及其对应的y碎片离子y到y，并与kahalalide S的MS/MS模式进行比较，确定脯氨酸可以被酪氨酸氨基酸残基取代。b（质荷比511）和b（质荷比674）之间的质量差等于163，这相当于酪氨酸的质量残基。它们的y碎片离子也很快有助于解开谜团。这导致鉴定出新的环缩肽kahalalide Z的肽序列为环-[Val-(5-甲基己基-Val-Thr-Val-Val-Tyr-Lys-Ile)Thr-Ile-Val-Phe-Dhb)]。因此，ESI-MS/MS为快速鉴定新的海洋分子开创了一种趋势。
