Selenotrisulfide as a Metabolic Intermediate in Biological Systems

In 1941, Painter showed that the reaction of selenious acid with low mass thiols (RSH) produced selenotrisulfide in vitro. Later, the reactivity of glutathione selenotrisulfide (GSSeSG) with thiols of pancreatic ribonuclease in an acidic medium was characterized by Ganther. Recently, several RSSeSR species were actually identified in biological systems by modern mass spectrometry. Due to the reversibility of the thiol exchange reaction, RSSeSR′ is generated from the reaction of RSSeSR with R′SH, when increasing the molar ratio of R′SH to RSSeSR. On the basis of these facts, we investigated the molecular events of the biogenic thiol-associated selenium transfer in the bloodstream, with particular attention to selenotrisulfide. We demonstrated that the selenium transfer from red blood cells to hepatocytes involves a relay mechanism of thiol exchange that occurs between the selenotrisulfide and thiols (RSSeSR + R′SH → R′SSeSR + R″SH → R′SSeSR″).