DIOXYGENASE AND CO-OXIDASE ACTIVITIES OF RAT HEPATIC CYTOSOLIC LIPOXYGENASE

The role of rat liver cytosolic lipoxygenase in the metabolism of benz idine was studied using linoleic acid as a cosubstrate. Under optimum assay conditions, cytosolic dioxygenase activity in the presence of 3. 5 mM linoleic acid at pH 7.2 was 74.07 +/- 1.43 nmoles/min/mg protein. Benzidine was oxidized at the rate of 3.18 +/- 0.13 nmoles/min/mg cyt osolic protein to benzidine diimine at pH 7.2 in the presence of 3.65 mM linoleic acid. Both dioxygenase and co-oxidase reactions were inhib ited by nordihydroguaiaretic acid in a concentration-dependent manner. Partially purified preparations of rat liver lipoxygenase, free of he moglobin, exhibited a dioxygenase activity of 223.1 +/- 65.9 nmoles/mi n/mg protein and co-oxidase activity of 6.1 +/- 0.5 nmoles/min/mg prot ein toward benzidine. These results suggest that hepatic lipoxygenase may play an important role in the metabolism of this hepatocarcinogen.