SUMMARY Propionyl carboxylase from bovine liver mitochondria has been further purified by the use of diethylaminoethyl (DEAE)- cellulose ion exchange chromatography. 2 Report by Dr. S. Ochoa at the Symposium on Metabolic Re- actions Involving Biotin, 137th meeting of the American Chemical Society, Cleveland, 1960. Methybnalonyl-CoA-3-W decarboxylated’ m~moles 0 0 1 2 27 28 8 8 19 17 %t 0 4 83 24 55 * Following incubation, acidified aliquots of the reaction mix- ture were plated and counted acaording to the procedure used for the Cl402 fixation assay (4). The residual radioactivity was con- verted to mpmoles by dividing by the specific activity of methyl- malonyl-CoA-3-W. t Average of duplicates. TABLE VI Effect of arsenate on carboxylation oj propionyl-CoA The reaction mixture contained (in rmoles) : Tris, pH 8.5, 100; propionyl-CoA, 1; ATP and MgC12, 4; GSH, 5; KHW03, 15; and ammonium sulfate-purified carboxylase, 0.05 mg. NazHAs04 added as indicated. Final volume, 1.5 ml. Incubated 20 min- utes at 37”.