Stability and nonreactivity of ergothioneine in human erythrocytes studied by 1H NMR

Abstract

The N(CH3)3 resonance of ergothioneine in 1H spin-echo Fourier transform (SEFT) NMR spectra of red blood cells is usually a large singlet and it has been common practice to use this apparently unchanging resonance as an intensity reference. Recently, Reglinski et al. (Magn. Reson. Med. 6, 217-223 (1988)) have questioned this practice, reporting changes seen in the resonance in response to oxidative stress induced by arsenicals. We propose that the changes in the ergothioneine resonance that were reported are artifacts due to alterations in osmolality and magnetic susceptibility induced by the addition of nonisotonic solutions to red blood cell suspensions. These factors change the specific intensity of the intracellular resonances of all compounds. Ergothioneine was observed not to take part in any chemical reactions with arsenicals in free solution or in intact erythrocytes, and we conclude that ergothioneine may still be used as an internal intensity reference in 1H SEFT NMR spectra, bearing in mind the above physical factors.