Purification of dopa decarboxylase from bovine striatum

Pyridoxal phosphate-dependent DOPA decarboxylase has been purified from bovine striatum to a specific activity of 1.6 U/mg protein. After ammonium sulfate precipitation (30-60%) it was purified by DEAE-Sephacel, Sephacryl S-200, and TSK Phenyl 5 PW chromatography. The purified enzyme showed a single silver straining band with polyacrylamide gel electrophoresis under both denaturing and non-denaturing conditions. The bovine striatal DOPA decarboxylase is a dimer (subunit Mr = 56,000 by SDS-PAGE) with a native Mr of 106,000 as judged by chromatography on Sephacryl S-200 and by sedimentation analysis. Similar to the DOPA decarboxylase purified from non-CNS tissues, the bovine striatal enzyme requires free sulfhydryl groups for activity, is strongly inhibited by heavy metal ions, and can decarboxylate 5-hydroxytryptophan as well. It should be noted, however, that the final enzyme preparation is enriched in DOPA decarboxylase activity. The distribution of the DOPA decarboxylase and 5-HTP decarboxylase activities also varies among several bovine brain regions. In addition, heat treatment of the enzyme preparation inactivated the two decarboxylation activities at different rates.