A chemical modification to make horseradish peroxidase soluble and active in benzene.

Horseradish peroxidase was modified with 2,4-bis(O- methoxypolyethylene glycol)-6-chloro-s-triazine. The modified peroxidase, in which 60% of the amino groups were coupled with polyethylene glycol, had 70% of the enzymic activity in aqueous solution and was found to be soluble in benzene. Since the modified peroxidase in benzene had an absorption spectrum similar to that of unmodified peroxidase in aqueous solution, the prosthetic group, protohaemin IX, remained with the apoprotein even in benzene. The modified peroxidase in benzene had 21% of the enzymic activity relative to that of unmodified enzyme in aqueous solution.