Liquid chromatography-mass spectrometry.

Duplicate reactions were prepared under optimal assay conditions for each recombinant enzyme. For pH under 7, 20 mM sodium acetate buffers were used, for pH 7 an ammonium chloride buffer was chosen. Samples were taken at different reaction times (5, 10, 20, 60, and 120 min). The reactions were stopped by heating the samples at 95°C for 5 min. Final sample preparation and liquid chromatography-mass spectrometry analysis was carried out as previously described (18).