Adducts of the chloroform metabolite phosgene

Detection of a glutathionyl-carbonylated group (GS-CO-) on D-dopachrome tautomerase with preferential binding of GS-CO- to MIF proteins in rat livers damaged by carbon tetrachloride

Liver damage has been induced in animal experiments using carbon tetrachloride (CCl₄), a potent hepatotoxin. CCl₄ is activated by cytochrome P450 2E1, which results in the formation of various metabolites including phosgene. Although D-dopachrome tautomerase (DDT) is abundant in the liver, its role currently remains unclear. The biological activity of DDT, for which the N-terminal proline is a key site, has been detected in various tissues. We herein incidentally detected a 333 Da modification to the N-terminal proline of DDT in rat livers damaged by CCl₄. We identified that this modification as glutathionyl carbonylated group, which was formed by condensation of phosgene and reduced glutathione (GSH). We examined other glutathionyl-carbonylated proteins using two dimensional-polyacrylamide gel electrophoresis, mass spectrometry, and Western blotting for GSH, and detected only one glutathionyl-carbonylated protein, macrophage migration inhibitory factor (MIF). DDT belongs to the MIF family of proteins, and amino acid sequence identity between DDT and MIF is 33%. We concluded that MIF family proteins are major targets for glutathionyl carbonylation.

Noteworthy Chemistry of Chloroform

Inhaled chloroform anesthesia was introduced in 1847. Soon thereafter, the chemical reactivity of aerobically heated chloroform permitted John Snow and Claude Bernard to do seminal experiments in the assay of drug levels and drug metabolism. However, it was not widely appreciated until a clinical mishap in 1899 that thermal decomposition generated significant levels of toxic phosgene from air-polluting quantities of chloroform in poorly ventilated operating rooms that were illuminated by flames. Phosgene is also generated metabolically from chloroform. A clue appeared in the 1950s when subanesthetic traces of inhaled chloroform proved accidentally lethal to strains of male mice spontaneously expressing high levels of chloroform-metabolizing enzymes. Furthermore, in microbial experiments of 1967, the reactive chloroform molecule was inadvertently discovered to selectively inactivate vitamin B12-dependent enzymes. Chloroform can also activate enzymes. As a solvent, it was serendipitously found in 1903 to activate what is now known as plasminogen to plasmin.