Methylmercury-cysteinylglycine constitutes the main form of methylmercury in rat bile.

The chemical form of methylmercury (MM) in bile was studied by gel filtration and ion exchange chromatography using male rats of various ages. EDTA was added to all mixtures used throughout the experimental procedures in order to prevent oxidation of non-protein sulfhydryl compounds (NPSHs). MM-cysteinylglycine (CysGly) was found to be a predominant chemical form of MM in bile of 4 to 22-week-old rat exposed to methylmercuric chloride. The ratio of MM-glutathione (GSH) tended to increase with age after 4 weeks until 12 weeks of age, reflecting the age-dependent increase in the ratio of GSH to total NPSHs in bile. In 8-week-old rats, although the biliary concentration of GSH was about three times higher than that of CysGly, MM-CysGly was still one of the main chemical forms of MM in bile. This suggests that CysGly has a higher affinity for MM than GSH. In fact, when MM was mixed in vitro with GSH and CysGly in the same molar ratio as that in the bile of 8-week-old rat, MM-CysGly was found to be a predominant mercury-thiol complex. Thus, age-dependent changes in the molar ratio of biliary NPSHs together with their affinity to MM seems to determine the biliary chemical form of MM administered or added into the bile in vitro.