Pyridoxine kinase, pyridoxine phosphate phosphatase and pyridoxine phosphate oxidase activities in control and B-6-deficient rat liver and brain.

The levels of pyridoxal phosphate in plasma, liver and brain and the activities of pyridoxine kinase, pyridoxine phosphate phosphatase and pyridoxine phosphate oxidase in liver and brain were measured over a 6-week period in rats fed pyridoxine-sufficient and pyridoxine-deficient diets. Consistently significant differences in enzyme activities between the two groups of animals were found only in pyridoxine kinase indicating that this enzyme plays a key role during the development of vitamin B-6 deficiency. Relative to control animals, the decrease observed in liver pyridoxine kinase acivity in animals fed pyridoxine-deficient diets is much greater than the decrease in brain pyridoxine kinase activity (50% decrease versus a 14% decrease after 5 weeks). In light of the suggestion that phosphorylation and binding to proteins serve to prevent the diffusion of B-6 vitamers out of cells, the differential response of pyridoxine kinase activity in liver and brain may be important in the maintenance of the vitamin B-6 supply in the central nervous system. During the course of this study, a new method for the determination of cellular phosphatase activity on a phosphorylated form of vitamin B-6 was developed. 3H-C4'-Pyridoxine phosphate was used as substrate and was separated from 3H-C4'-pyridoxine by means of anion-exchange filter paper disks.