Purification and structure of the major product obtained by reaction of NADPH and NMNH with the myeloperoxidase/hydrogen peroxide/chloride system

The first spectrophotometric study of the reaction of the myeloperoxidase/H 2O2/Cl- system with NADPH and NMNH showed that the reaction products were n ot the corresponding oxidized nucleotides and that modifications would take place on the nicotinamide part of the molecule [Auchere, F. & Capeillere-B landin, C. (1999) Biochem. J. 343, 603-613]. In this report, in order to ob tain more precise information on the structural modifications and mechanism of the reaction, we focus on the purification and isolation of products de rived from NADPH and NMNH by RP-HPLC. Electrospray ionization mass spectra indicated that the relative height of the peaks reflected that of the natur al isotopic abundance of Cl-35 and Cl-37, providing evidence that the produ cts derived from NADPH and NMNH were monochlorinated. Moreover, calculated masses revealed the 1 : 1 addition of HOCl to the molecule. Various 1D and 2D NMR experiments provided data for the assignments of the chemical shifts of protons and carbons and the coupling constants of the protons of the ch lorinated nucleotides. Further NOESY experiments allowed the characterizati on of the spatial structure of the chlorinated product and showed that tran s HOCl addition occurred at the C5=C6 carbon double bond of the nicotinamid e ring, leading to a chlorohydrin.