The tripeptide glutathione (GSH) is present in cells at millimolar concentrations, and the ratio of GSH to glutathione disulfide (GSSG) is critical to cellular redox balance. Changes in the cell redox status may induce reversible formation of mixed disulfides between protein sulfhydryl groups and glutathione (S-glutathionylation) on multiple proteins, which makes of cellular glutathione a crucial modulating factor for an ever increasing number of proteins. In particular protein S-glutathionylation can occur by reaction between protein thiols and nitrosoglutathione (GSNO). Results of a previous experiment on GSH unexpectedly indicated a weak H-bond between its sulfhydryl group and water. We want to test the hypothesis that this weak H-bond is functional, if water has to be replaced with nitric oxide resulting in the formation of GSNO.