Pantothenoylcysteine‐4′‐phosphate Decarboxylase from Horse Liver

Pantothenoylcysteine‐4′‐phosphate decarboxylase has been purified 700‐fold from horse liver by by an improved method. Enzyme activity was determined by measuring the amount of labeled CO2 produced from the labeled cysteine moiety of the substrate molecule. The enzyme is not bound to any cellular structure since more than 80% of the total activity of the homogenate is recovered in the supernatant fraction. The enzyme does not seem to contain pyridoxal phosphate, is strongly inhibited by this latter and by carbonyl reagents, such as sodium borohydride, hydroxylamine and phenylhydrazine. These findings strongly support the presence in the enzyme molecule of a reactive carbonyl group. The enzymic reaction rate is increased over 20‐fold by sulfhydryl compounds, has an absolute specificity for pantothenoylcysteine 4′‐phosphate and is not inhibited either by pantothenoylcysteine or by the reaction product, pantetheine 4′‐phosphate.