Tholey A, Reed J, Lehmann W D
Department of Pathochemistry, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany.
J Mass Spectrom. 1999 Feb;34(2):117-23. doi: 10.1002/(SICI)1096-9888(199902)34:2<117::AID-JMS769>3.0.CO;2-V.
A set of synthetic phosphopeptides and phosphopeptide analogues was studied by tandem nano-electrospray mass spectrometry. The influence of the collision offset and of the charge state of the molecular ion on phosphate-specific fragmentation processes was investigated in detail. H--D exchange experiments and structural considerations support a six-centered transition being present in the neutral loss of H3PO4 from serine, threonine and homoserine phosphopeptides, where the C-alpha hydrogen of serine or threonine or the C-beta hydrogen of homoserine is transferred to the protonated phosphate group. Neutral loss of H3PO4 at moderate collision offset potential represents a very abundant fragmentation process for serine, threonine and homoserine phosphopeptides. The most specific feature for discrimination of these phosphopeptides from tyrosine phosphopeptides is the m/z 79:97 ratio in the negative ion product spectra, which is consistently elevated in tyrosine phosphopeptides as compared with serine, threonine and homoserine phosphopeptides. The fragment ions of methylphosphono- and H-phosphonopeptides can be explained by the same mechanisms as are applicable to phosphopeptides.
通过串联纳米电喷雾质谱对一组合成的磷酸肽和磷酸肽类似物进行了研究。详细研究了碰撞偏移和分子离子电荷状态对磷酸特异性裂解过程的影响。氢-氘交换实验和结构分析支持在丝氨酸、苏氨酸和高丝氨酸磷酸肽中H3PO4中性丢失过程中存在六中心过渡态，其中丝氨酸或苏氨酸的α-碳氢或高丝氨酸的β-碳氢转移至质子化的磷酸基团。在适度碰撞偏移电位下H3PO4的中性丢失是丝氨酸、苏氨酸和高丝氨酸磷酸肽非常丰富的裂解过程。将这些磷酸肽与酪氨酸磷酸肽区分开来的最特异性特征是负离子产物谱中m/z 79:97的比值，与丝氨酸、苏氨酸和高丝氨酸磷酸肽相比，酪氨酸磷酸肽中的该比值持续升高。甲基膦酸肽和氢膦酸肽的碎片离子可用与磷酸肽相同的机理解释。
