Isolation and characterization of horseradish peroxidase compound X

Horseradish peroxidase reacts with sodium [36Clll] chlorite at pH 10.7 to form a 36Cl-labeled horseradish peroxidase intermediate. The optical absorption spectrum of this intermediate is quite stable and very similar to that of horseradish peroxidase Compound II. The intermediate can be separated from small molecules by chromatography on a Sephadex G-10 column. After fractionation, 65 to 93% of 36Cl in the reaction mixture remains associated with horseradish peroxidase. The remainder of 36Cl-labeled enzyme reacts with 5,5-dimethyl-2-chloro-1,3-cyclohexanedione (monochlorodimedone) at pH 4 to transfer 36Cl from the enzyme to the halogen acceptor molecule. [36C]5,5-Dimethyl-2,2-dichloro-1,3-cyclohexanedione (dichlorodimedone) was established as the major product of the transfer reaction by co-crystallization of the enzymic product with authentic dichlorodimedone and by thin layer chromatography. A chlorine oxide ligand on a ferryl heme iron protoporphyrin IX is proposed for the structure of Compound X.