Vitamin B-6 metabolism and its relation to ornithine decarboxylase activity in regenerating rat liver

The metabolism of vitamin B-6 regenerating rat liver and liver from sham-operated control animals fed either a pyridoxine-sufficient or pyridoxine-deficient was investigated. The pyridoxal phosphate levels in plasma, regenerating liver and control liver were determined as were the activities of three enzymes involved in the metabolism of the vitamin, namely, pyridoxine kinase, pyridoxine phosphate oxidase, and pyridoxine phosphate phosphatase. In addition, total and holo-ornithine decarboxylase activities in the livers were measured. The results indicate that the metabolism of vitamin B-6 regenerating rat liver is different from that observed in Morris hepatomas (Thanassi et al. (1981) J. Biol. Chem. 256, 3370-3375). Vitamin B-6 metabolism in Morris hepatomas is concluded to be characteristic of the tumors rather than a property common to rapidly proliferating hepatic tissue. Regenerating liver ornithine decarboxylase holoenzyme activity in pyridoxine deprived rats was maintained at the same level as that in regenerating liver of pyridoxine-sufficient animals. The mechanism behind this maintenance of holo-enzyme activity appears to involve a pronounced increase in the amount of apoornithine decarboxylase. The time-dependent peak of ornithine decarboxylase activity following partial hepatectomy was shifted from four hours to twelve hours by vitamin B-6 deficiency.