3-Hydroxy-4-nitrobenzoic Acid as a MALDI Matrix for In-Source Decay
2016
Fukuyama, Yuko | Izumi, Shunsuke | Tanaka, Kōichi
In-source decay (ISD) in matrix-assisted laser desorption/ionization (MALDI) is a rapid sequencing method for peptides. 1,5-Diaminonaphthalene (1,5-DAN) is a most frequently used matrix for ISD. However, using 1,5-DAN generates mainly c- and z-series ions by N–Cα bond cleavage, which makes it difficult to distinguish leucine (Leu) and isoleucine (Ile), and frequently lacks c₍ₙ–₁₎-series ions owing to proline (Pro) at residues n. Several oxidizing matrices generating a- and x-series ions accompanied by d-series ions by Cα–C bond cleavage have been reported, but an issue remained concerning their sensitivity. 3-Hydroxy-4-nitrobenzoic acid (3H4NBA) has been reported as a matrix for 2-nitrobenzenesulfenyl-labeled peptides by Matsuo et al. (Proteomics 2006, 6, 2042–2049). Here, we used 3H4NBA as an oxidizing matrix for ISD. As a result, numerous a- and d-series ions for amyloid β 1–40 were generated with high sensitivity using 3H4NBA. Each of the two Leu and two Ile was identified by the d-series ions. The sensitivity of the a-series ions using 3H4NBA was a little lower than that of c-series ions using 1,5-DAN. The same tendency was observed for N-acetyl renin substrate and ACTH 18–39. The a-series ions were detected, even at the left side of Pro. The sensitivity of the a-series ions using 3H4NBA was higher than with other existing oxidizing matrices, such as 5-nitrosalicylic acid and 5-formyl salycilic acid. The ions were detected over the entire area of the matrix-analyte spot using 3H4NBA. 3H4NBA was confirmed to be a useful oxidizing matrix for ISD, leading to higher sequence coverage of peptides.
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