Specific Antiserum and Monoclonal Antibodies Against the Taurine Biosynthesis Enzyme Cysteine Sulfinate Decarboxylase: Identity of Brain and Liver Enzyme

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Abstract
Cysteine sulfinate decarboxylase (CSD), the putative biosynthetic enzyme for taurine, was purified 1,800‐fold with a 1% yield from rat liver, where it was found to be 20‐fold enriched compared with brain. The final fraction was homogeneous, as ascertained through sodium dodecyl sulfatepolyacrylamide gel electrophoresis and reverse‐phase HPLC. An antiserum was raised in the rabbit that (a) quantitatively immunoprecipitated CSD activity and (b) immunolabeled only one band (MW = 51,000) on an immunoblot from liver homogenate. Monoclonal antibodies were also raised that recognized the CSD protein and immunolabeled the same 51‐kilodalton protein on an immunoblot from liver homogenate. In a brain extract, two CSD activities had been previously found and named CSDI and CSDII, according to their chromatographic elution patterns. We have compared the properties of CSDI from brain–the most likely enzyme involved in the biosynthesis of taurine in the brain, according to previous investigations–and CSD from liver: Both activities (a) were similarly eluted on ion‐exchange and hydroxyapatite chromatographies, (b) showed the same elution pattern on gel filtration with an apparent native molecular weight of ˜63,000, and (c) were immunoprecipitated in a strictly identical manner by the antiserum against liver CSD. Moreover, this antiserum as well as the monoclonal antibodies immunolabeled a single band (51 kilodaltons) on an immunoblot from brain CSD‐enriched fraction or liver fraction. All these data show that CSDI from brain and liver CSD are the same monomeric enzyme. They also indicate that a specific antiserum against rat liver CSD has been raised that can be used for the immunocytochemical visualization of CSD‐containing cells in the brain.