抄録
Permeability of vitamin B6in human erythrocytes and that in ascites-sarcoma cells were studied in vitro. Furthermore, the transport system of this vitamin was investigated by using the method of perfused rat liver.
1. Transport of vitamin B6 in human erythrocytes: Free forms of vitaminB6 were transported into erythrocytes against the concentration gradient, in particular pyridoxal was migrated in a large amount and very rapidly. In the case of vitamin B6phosphates, the transported amount in erythrocytes was very small as compared with the free forms of B6. Under the effect of the phosphate concentration on the transport of free and phosphorylated forms of B6into erythrocytes, the rates of transfer for pyridoxine, pyridoxamine and pyridoxal phosphate were lowered upon decrease in phosphate concentration in the medium, while that for pyridoxal was not. Potassium fluoride (50mM) inhibited the transport of pyridoxine, pyridoxamine and pyridoxal phosphate, but did not that of pyridoxal. In the presence of desoxy-pyridoxine, the transported amounts of pyridoxine and pyridoxamine were decreased competitively, while the amounts of pyridoxal and pyridoxal phosphate were not.
2. Uptake of vitamin B6 in ascites-sarcoma cells: When ascites-sarcoma cells were incubated with pyridoxine-14C, concentration of total labelled B6in the cell was higher than that in the medium. Separate analysis of free and phosphorylated forms of B6 in a cellular extract showed that the transported pyridoxine was phosphorylated in the cells in a constant amount. Addition of 2, 4-dinitrophenol (0.5 mM) inhibited the uptake of pyridoxine in the cells, but that of pyridoxal was not inhibited. In the presence of desoxy-pyridoxine, the uptake of pyridoxine was inhibited, but the inhibition was not observed in pyridoxal. Incubation at 37°C of ascitessarcoma cells in Krebs-Ringer phosphate medium containing pyridoxal phosphate resulted in accumulation of pyridoxal phosphate in the cells and this accumulation was not affected by the addition of glucose and 2, 4-dinitrophenol.
3. Transport system of different forms of B6 By means of the method of perfused rat liver, the transport system of different forms of B6was investigated and the following observation was obtained. Pyridoxal phosphate, which scarcely penetrates into erythrocytes, is transported in the forms bounded with albumin and utilized in various tissue cells with albumin. Free forms of B6 is transported actively into erythrocytes. But other portions contained in plasma is phosphorylated in the liver and transported in the form bounded with albumin. The elevating amounts of B6phosphates in normal perfused rat liver are much smaller than that in perfusate.
