The oxidation and decarboxylation of retinoic acid by horseradish peroxidase

The decarboxylation of retinoic acid by horseradish peroxidase was investigated. A marked increase in the yield of products was obtained. However, the data indicated the reaction was a nonenzymatic, heme catalyzed peroxidation. Previously reported requirements for phosphate, oxygen and ferrous ion were eliminated when hydrogen peroxide was provided. Peroxide also eliminated the EDTA and cyanide induced inhibition of the phosphate dependent system. In the presence of hydrogen peroxide, horseradish peroxidase was not essential to the reaction; heme equivalent amounts of hemoglobin decarboxylated retinoic acid with equal facility. However, hemoglobin was ineffective in the absence of hydrogen peroxide. Attainment of 50--60% decarboxylation represented complete utilization of the available retinoic acid. Thus the products of the reaction can be divided into two groups, products of retinoic acid oxidation and products of an oxidative decarboxylation of retinoic acid.