   2.6.1.B16 | pyruvate + (S)-1-phenylethylamine = L-alanine + acetophenone |
reaction mechanism for the half-transamination of L-alanine to pyruvate in (S)-selective Chromobacterium violaceum omega-transaminase by density functional theory calculations, role of a flexible arginine residue, Arg416, in the dual-substrate recognition. The amine is kinetically favored in the half-transamination of L-alanine/pyruvate, whereas the ketone is kinetically favored in the half-transamination of (S)-1-phenylethylamine/acetophenone. The arginine residue facilitates the dual-substrate recognition by functioning as an arginine switch, where the side chain is positioned inside or outside of the active site depending on the substrate. Arg416 participates in the binding of L-alanine by forming a salt bridge to the carboxylate moiety, whereas the conversion of (S)-1-phenylethylamine is feasible in the absence of Arg416, which here represents the case in which the side chain of Arg416 is positioned outside of the active site. Many PLP-dependent enzymes, including transaminases, require the formation of a so-called internal aldimine (E-PLP), before the main reaction. In this process, the PLP coenzyme becomes covalently bound to an active-site lysine residue as a protonated Schiff base, which constitutes the active form of the enzyme. The transamination reaction consists of two half-transamination equilibria. An amino donor is converted to the corresponding ketone or aldehyde, resulting in the conversion of E-PLP to pyridoxamine-5'-phosphate (PMP). The E-PLP is then regenerated by the reaction of another ketone or aldehyde, which is then converted to an amine |
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