Abstract
The importing of vitamin B6 by renal proximal tubular cells from the rat is facilitated and Na(+)-dependent and reflects specificity for the meta-phenolate pyridinium structure with a 5-hydroxymethyl function. This transporter can, however, accept competitively each of the natural nonphosphorylated vitamers (pyridoxine, pyridoxamine, and pyridoxal) and other B6 analogues differing only in the groups at position 4. A series of N-(4'-pyridoxyl)amines was synthesized by sodium borohydride or boro[3H]hydride reduction of aldimines formed by condensing the amines with pyridoxal. The unlabeled B6-secondary amine compounds were found to competitively inhibit the uptake of [4'-3H]pyridoxine by the renal cells. Moreover, the 3H-labeled N-(4'-pyridoxyl)amines were shown to enter the cells by the process facilitated by the B6 transporter. Upon entry the labeled compounds were converted to N-(5'-phospho-4'-pyridoxyl)amines in a reaction catalyzed by pyridoxal kinase, an enzyme that tolerates considerable functional variation in position 4 of the B6 structure. The 5'-phosphates were subsequently converted within the cell to pyridoxal 5'-phosphate with liberation of the original amine in a reaction catalyzed by pyridoxamine (pyridoxine) 5'-phosphate oxidase, an enzyme with broad specificity for 4'-substituted amines on the 5'-phospho-B6 structure. This system illustrates how knowledge of transporter specificity can permit design of a compound with potential biologic activity. A drug or other intracellular effector may be piggybacked onto a transported solute (e.g., vitamin or other nutrient) that gains facilitated entry to a cell and is, thereafter, metabolized to release the active compound.
Full text
PDF![10407](https://cdn.ncbi.nlm.nih.gov/pmc/blobs/76de/52937/437b23a0b335/pnas01073-0042.png)
![10408](https://cdn.ncbi.nlm.nih.gov/pmc/blobs/76de/52937/48bcec6125ca/pnas01073-0043.png)
![10409](https://cdn.ncbi.nlm.nih.gov/pmc/blobs/76de/52937/a98566045ced/pnas01073-0044.png)
![10410](https://cdn.ncbi.nlm.nih.gov/pmc/blobs/76de/52937/a79a792e5c5f/pnas01073-0045.png)
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Aw T. Y., Jones D. P., McCormick D. B. Uptake of riboflavin by isolated rat liver cells. J Nutr. 1983 Jun;113(6):1249–1254. doi: 10.1093/jn/113.6.1249. [DOI] [PubMed] [Google Scholar]
- Bowers-Komro D. M., McCormick D. B. Biotin uptake by isolated rat liver hepatocytes. Ann N Y Acad Sci. 1985;447:350–358. doi: 10.1111/j.1749-6632.1985.tb18450.x. [DOI] [PubMed] [Google Scholar]
- Bowers-Komro D. M., McCormick D. B. Characterization of ascorbic acid uptake by isolated rat kidney cells. J Nutr. 1991 Jan;121(1):57–64. doi: 10.1093/jn/121.1.57. [DOI] [PubMed] [Google Scholar]
- Bowers-Komro D. M., McCormick D. B. Pyridoxamine-5'-phosphate oxidase exhibits no specificity in prochiral hydrogen abstraction from substrate. J Biol Chem. 1985 Aug 15;260(17):9580–9582. [PubMed] [Google Scholar]
- Bowman B. B., McCormick D. B. Pyridoxine uptake by rat renal proximal tubular cells. J Nutr. 1989 May;119(5):745–749. doi: 10.1093/jn/119.5.745. [DOI] [PubMed] [Google Scholar]
- Bowman B. B., McCormick D. B., Rosenberg I. H. Epithelial transport of water-soluble vitamins. Annu Rev Nutr. 1989;9:187–199. doi: 10.1146/annurev.nu.09.070189.001155. [DOI] [PubMed] [Google Scholar]
- Bowman B. B., McCormick D. B., Smith E. R. Vitamin B6 uptake by rat kidney cells and brush-border membrane vesicles. Ann N Y Acad Sci. 1990;585:106–109. doi: 10.1111/j.1749-6632.1990.tb28046.x. [DOI] [PubMed] [Google Scholar]
- Bradford M. M. A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal Biochem. 1976 May 7;72:248–254. doi: 10.1016/0003-2697(76)90527-3. [DOI] [PubMed] [Google Scholar]
- DePecol M. E., McCormick D. B. Syntheses, properties, and use of fluorescent N-(5'-phospho-4'-pyridoxyl)amines in assay of pyridoxamine (pyridoxine) 5'-phosphate oxidase. Anal Biochem. 1980 Jan 15;101(2):435–441. doi: 10.1016/0003-2697(80)90210-9. [DOI] [PubMed] [Google Scholar]
- Jones D. P., Sundby G. B., Ormstad K., Orrenius S. Use of isolated kidney cells for study of drug metabolism. Biochem Pharmacol. 1979 Mar 15;28(6):929–935. doi: 10.1016/0006-2952(79)90378-2. [DOI] [PubMed] [Google Scholar]
- Kazarinoff M. N., McCormick D. B. N-(5'-phospho-4'-pyridoxyl)amines as substrates for pyridoxine (pyridoxamine) 5'-phosphate oxidase. Biochem Biophys Res Commun. 1973 May 15;52(2):440–446. doi: 10.1016/0006-291x(73)90731-6. [DOI] [PubMed] [Google Scholar]
- Kazarinoff M. N., McCormick D. B. Rabbit liver pyridoxamine (pyridoxine) 5'-phosphate oxidase. Purification and properties. J Biol Chem. 1975 May 10;250(9):3436–3442. [PubMed] [Google Scholar]
- Kozik A., McCormick D. B. Mechanism of pyridoxine uptake by isolated rat liver cells. Arch Biochem Biophys. 1984 Feb 15;229(1):187–193. doi: 10.1016/0003-9861(84)90143-7. [DOI] [PubMed] [Google Scholar]
- MCCORMICK D. B., GREGORY M. E., SNELL E. E. Pyridoxal phosphokinases. I. Assay, distribution, I. Assay, distribution, purification, and properties. J Biol Chem. 1961 Jul;236:2076–2084. [PubMed] [Google Scholar]
- MCCORMICK D. B., SNELL E. E. Pyridoxal phosphokinases. II. Effects of inhibitors. J Biol Chem. 1961 Jul;236:2085–2088. [PubMed] [Google Scholar]
- McCormick D. B., Snell E. E. PYRIDOXAL KINASE OF HUMAN BRAIN AND ITS INHIBITION BY HYDRAZINE DERIVATIVES. Proc Natl Acad Sci U S A. 1959 Sep;45(9):1371–1379. doi: 10.1073/pnas.45.9.1371. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Ormstad K., Orrenius S., Jones D. P. Preparation and characteristics of isolated kidney cells. Methods Enzymol. 1981;77:137–146. doi: 10.1016/s0076-6879(81)77018-6. [DOI] [PubMed] [Google Scholar]
- Rose R. C., McCorrmick D. B., Li T. K., Lumeng L., Haddad J. G., Jr, Spector R. Transport and metabolism of vitamins. Fed Proc. 1986 Jan;45(1):30–39. [PubMed] [Google Scholar]
- Voet J. G., Hindenlang D. M., Blanck T. J., Ulevitch R. J., Kallen R. G., Dunathan H. C. The stereochemistry of pyridoxal phosphate enzymes. The absolute stereochemistry of cofactor C' 4 protonation in the transamination of holoserine hydroxymethylase by D-alanine. J Biol Chem. 1973 Feb 10;248(3):841–842. [PubMed] [Google Scholar]