Real-time NMR monitoring of intermediates and labile products of the bifunctional enzyme UDP-apiose/UDP-xylose synthase

The conversion of UDP-α-d-glucuronic acid to UDP-α-d-xylose and UDP-α-d-apiose by a bifunctional potato enzyme UDP-apiose/UDP-xylose synthase was studied using real-time nuclear magnetic resonance (NMR) spectroscopy. UDP-α-d-glucuronic acid is converted via the intermediate uridine 5′-β-l-threo-pentapyranosyl-4″-ulose diphosphate to UDP-α-d-apiose and simultaneously to UDP-α-d-xylose. The UDP-α-d-apiose that is formed is unstable and is converted to α-d-apio-furanosyl-1,2-cyclic phosphate and UMP. High-resolution real-time NMR spectroscopy is a powerful tool for the direct and quantitative characterization of previously undetected transient and labile components formed during a complex enzyme-catalyzed reaction.

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