Andreazza Hayley J, Wang Tianfang, Bagley Christopher J, Hoffmann Peter, Bowie John H
Department of Chemistry, The University of Adelaide, South Australia, 5005, Australia.
Rapid Commun Mass Spectrom. 2009 Jul;23(13):1993-2002. doi: 10.1002/rcm.4107.
The following peptides have been examined in this study: GLDFG(OH), caeridin 1.1 [GLLDGLLGLGGL(NH(2))], 11 Ala citropin 1.1 [GLFDVIKKVAAVIGGL(NH(2))], Crinia angiotensin [APGDRIYVHPF(OH)] and their isoAsp isomers. It is not possible to differentiate between Asp- and isoAsp-containing peptides (used in this study) using negative ion electrospray mass spectrometry. This is because the isoAsp residue cleaves to give the same fragment anions as those formed by delta and gamma backbone cleavage of Asp. The isoAsp fragmentations are as follows: RNHCH(CO(2)H)(-)CHCONHR' --> [RNH(-)(HO(2)CCH=CHCONHR')] --> RNH(-)+HO(2)CCH=CHCONHR' and RNHCH(CO(2)H)(-)CHCONHR' --> [RNH(-)(HO(2)CCH=CHCONHR'] --> (-)O(2)CCH=CHCONHR'+RNH(2). Calculations at the HF/6-31+G(d)//AM1 level of theory indicate that the first of these isoAsp cleavage processes is endothermic (by +115 kJ mol(-1)), while the second is exothermic (-85 kJ mol(-1)). The barrier to the highest transition state is 42 kJ mol(-1). No diagnostic cleavage cations were observed in the electrospray mass spectra of the MH(+) ion of the Asp- and isoAsp-containing peptides (used in this study) to allow differentiation between these two amino acid residues.
GLDFG(OH)、caeridin 1.1 [GLLDGLLGLGGL(NH₂)]、11个丙氨酸的citropin 1.1 [GLFDVIKKVAAVIGGL(NH₂)]、Crinia血管紧张素 [APGDRIYVHPF(OH)] 及其异天冬氨酸异构体。使用负离子电喷雾质谱法无法区分本研究中使用的含天冬氨酸和含异天冬氨酸的肽。这是因为异天冬氨酸残基裂解产生的碎片阴离子与天冬氨酸的δ和γ主链裂解形成的碎片阴离子相同。异天冬氨酸的裂解过程如下：RNHCH(CO₂H)(-)CHCONHR' → [RNH(-)(HO₂CCH=CHCONHR')] → RNH(-)+HO₂CCH=CHCONHR' 以及 RNHCH(CO₂H)(-)CHCONHR' → [RNH(-)(HO₂CCH=CHCONHR'] → (-)O₂CCH=CHCONHR'+RNH₂。在HF/6 - 31 + G(d)//AM1理论水平上的计算表明，这些异天冬氨酸裂解过程中的第一个是吸热的（+115 kJ mol⁻¹），而第二个是放热的（-85 kJ mol⁻¹）。最高过渡态的势垒为42 kJ mol⁻¹。在本研究中使用的含天冬氨酸和含异天冬氨酸的肽的MH⁺离子的电喷雾质谱中未观察到诊断性裂解阳离子，无法区分这两个氨基酸残基。
