13C-NMR study of taurine and chlorotaurine in human cells.

13C-NMR with 13C-enriched taurine [( 13C]taurine) has been utilized to study the formation and reactions of N-chlorotaurine in solution and in human cells. Taurine reacts instantaneously with HOCl at pH 7.0 to form N-chlorotaurine, which is stable in solution by itself. In the presence of alpha-amino acids, a chlorine transfer reaction taken place to produce N-chloroamino acids, which quickly convert to the corresponding aldehydes. [13C]Taurine was incubated with human neutrophils and with cultured human lymphoblastoid cells and 13C-NMR spectra of the whole cell mixtures were acquired in order to examine the formation of N-chlorotaurine from reaction between taurine and the endogenous HOCl produced by myeloperoxidase-catalyzed reactions (Zgliczynski, J.M., et al. (1968) Eur. J. Biochem. 4, 540; Weiss, S.J., et al. (1982) J. Clin. Invest. 70, 598). The presence of N-chlorotaurine in the cells was not detected on the 13C-NMR spectra. On the other hand, N-chloro[13C]taurine incubated with the cells was found to be converted to taurine, which must have been produced by a chlorine transfer reaction of the N-chlorotaurine to other cellular components such as amino acids, peptides or proteins. A 13C-NMR study of taurine uptake in human lymphoblastoid cells indicated that taurine is incorporated into a freely mobile intracellular pool. These results suggest that the presence of abundant taurine in a freely mobile intracellular pool may serve as a buffer in preventing oxidative damage to the cells from attacks by HOCl or other oxidants.