Multiple step reactions: (a) schematic diagram of a simultaneous synthesis of (S)-amino acids and (R)-amine. Five different solutions were prepared for the two-step reactions: aspartate (Asp; 5 mM), α-ketoglutarate (α-KG; 5 mM), aspartate aminotransferase (Asp-AT; 5 U/ml), methylbenzylamine (MBA; 1 mM), and ω-aminotransferase (ω-AT; 3.75 U/ml); (b) mass spectrum of coupled enzyme reactions (two-step biochemical reaction); and (c) mass spectrum of coupled biochemical reactions and a chemical modification of acid (three-step biochemical reaction). The [Pyr-Q+H]+ and [KG-Q+H]+ indicated the quinoxalinol forms by phenylenediamine, and [KG-M+Na]+ indicated the matrix and sodium adduct of ketoglutarate
Figure 5 (a) shows the schematic diagram of the simultaneous
synthesis of (S)-amino acids and (R)-amine.
Figure 5 (b) shows the MALDI-MS spectrum of coupled enzyme
reactions such as the Asp-AT and ω-AT reactions.
The MALDI–MS spectrum [Fig. 5 (c)] shows the products of the
coupled enzyme reaction and the chemical modification of the
ketoacid, which suggests that the microfluidic chip offers useful
performance with multiple biochemical reactions, and that a
chemical modification step can be efficiently applied to MS
analysis of a ketoacid in the positive mode..
As described in Section 3.3 , for the on-chip reaction, only
a 300 nl sample solution was consumed during microfluidic
processes, despite which the reaction products, Ala and Glu, were
clearly detected in the MALDI–MS analysis, as shown in Fig. 5
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