Transport of Vitamin B₆ in Human Erythrocytes

Abstract

Free forms of B₆ are actively transported into the erythrocytes against a concentration gradient, especially, pyridoxal reaches quickly a level large enough to include permeation of all the cell water. Small amounts of pyridoxine and pyridoxal transported in the cells are in the phosphorylated forms. Decreasing the hydrogen ion concentration results in a decreased transportation of pyridoxine and pyridoxamine, but no decreased transportation of pyridoxal. Transported pyridoxine in the cells scarcely leaked out by the washing process, but a small amount of transported pyridoxal was eluted in the washing saline solution. The transported amounts of pyridoxine and pyridoxamine into the cells increase in accordance with the acceleration of intracellular glycolysis induced by the uptake of phosphate, while the transported amount of pyridoxal does not. Furthermore, the concentration of pyridoxal phosphate in the cells after an incubation with various forms of vitamin B₆ is decreased in parallel with the decreased amount of phosphate in the medium. In contrast, the transported amount of phosphorylated forms of B₆ into erythrocytes are much smaller than that of their free forms, although the transportation of pyridoxal phosphate in the cells increases in parallel with the elevation of the amount in the medium. The binding of pyridoxine and pyridoxal by the ghost cells is not observed. The ghost cells liberate enzymatically about 24% of pyridoxal from pyridoxal phosphate.