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Pyridoxine-5'-ß-D-Glucoside Competitively Inhibits Uptake of Vitamin B-6 into Isolated Rat Liver Cells¹

Department of Biochemistry, Rollins Research Center, Emory University, Atlanta, GA 30322 ^* Food Science and Human Nutrition Department, University of Florida, Gainesville, FL 32611-0370

Uptake of pyridoxine-5'-ß-D-glucoside by freshly isolated rat liver cells was studied at a concentration (0.5 µmol/L) approximating the physiological range of vitamin B-6 by using a membrane filtration method. Unlabeled pyridoxine glucoside was found to competitively inhibit the uptake of [4'-³H]pyridoxine but have no detectable effect on the uptake of D-[1-³H]glucose by hepatocytes. The uptake of [³H]pyridoxine glucoside by isolated rat liver cells was very similar to the uptake of [³H]pyridoxine with K_t = 13.8 µmol/L (6.3 µmol/L for pyridoxine) and V_max = 82 pmol/(10⁶ cells·min) [28 pmol/(10⁶ cells·min for pyridoxine)]. The results of this study indicate that pyridoxine glucoside uses the same transport system as does pyridoxine. Upon entry to the cell, pyridoxine glucoside undergoes hydrolysis to release pyridoxine, which is the rate-limiting step in metabolism of this ß-glucoside.

KEY WORDS: • pyridoxine glucoside • vitamin B-6 • uptake • hepatocyte • rats

¹ Supported by grants from the National Institutes of Health to D.B.M. (DK 43005) and to J.F.G. (DK 37481).

² To whom correspondence should be addressed.

Manuscript received 23 July 1992. Revision accepted 9 September 1992.

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