Stereochemistry of cysteinesulphinic acid decarboxylase

Abstract

An h.p.i.c.-based assay for cysteinesulphinic acid decarboxylase has been developed. The assay simultaneously measures glutamate decarboxylation and/or taurine formation. Using the cysteinesulphinic acid decarboxylase in rat liver homogenate, L-[2-²H₁]cysteinesulphinic acid was converted into [2-²H₁]hypotaurine. Similarly, unlabelled L-cysteinesulphinic acid was transformed by rat liver homogenate in a D₂O-containing medium into the enantiomeric [2-²H₁] hypotaurine. The products were desulphurized by treatment with Raney nickel, and the resulting enantiomeric [1-²H₁]ethylamines converted into the corresponding (–)-camphanamides. Deuterium n.m.r. spectra of the latter revealed that the decarboxylations proceeded stereospecifically with retention of configuration.