Pyridoxine glucosides

Recent interlaboratory comparisons of HPLC and microbiological methods for vitamin B6 revealed significant variability among laboratories (42,70). The extraction and hydrolysis of the B6 vitamers, especially the pyridoxine-/ -glucoside (PNG) in plant-based foods, were cited as problem areas. Other sources of analytical error included HPLC (mis)identification of the individual B6 vitamers, and vitamer interconversion during extraction and analysis. 

CM Hansen, JE Leklem, LT Miller. Vitamin B-6 status indicators decrease in women consuming a diet high in pyridoxine glucoside. J Nutr 126 2512-2518, 1996. 

DA Sampson, Q-B Wen, K Lorenz. Vitamin B6 and pyridoxine glucoside content of wheat and wheat flours. Cereal Chem 73 770-774, 1996. 

K Tadera, Y Naka. Isocratic paired-ion HPLC method to determine B6 vitamers and pyridoxine glucoside in foods. Agric Biol Chem 55 563-564, 1991. 

Six vitamers of Be, having equivalent biopotency, are found in nature [1,16] pyridoxine or pyridoxol, pyridoxal, pyridoxamine, and their 5 -phosphate esters acid pyridoxic and pyridoxine-glucoside are inactive forms occurring in plant tissues. Regulation 1925/2006/EC cites... 

Pyridoxine is present in food in the free form and as a glucoside, which may undergo partial hydrolysis in the gut lumen, or may be absorbed intact. Although pyridoxine is associated with the enzyme glycogen phosphorylase in muscles, it is not released in response to a dietary deficiency therefore it cannot be regarded as a storage form of the vitamin. 

JA Gilbert, JF Gregory. Pyridoxine-5 -/3-D-glucoside affects the metabolic utilization of pyridoxine in rats. J Nutr 122 1029-1035, 1992. 

ZZhang, JF Gregory, DB McCormick. Pyridoxine-5 -beta-D-glucoside competitively inhibits uptake of vitamin B-6 into isolated rat liver cells. J Nutr 123 85-89, 1993. 

McMahon, L., Nakano, H-, Levy, M.-D., and Gregory, J. F (1997). Cytosolic pyridoxine-p-D-glucoside hydrolase from porcine jejunal mucosa. /. Biol. Cfjcrn. 272,32025-32033. 

Nakano, H., McMahon, L.G., and Gregory, J.F., 1997. Pyridoxine-5 -B-D-glucoside exhibits incomplete bioavailability as a source of vitamin Bg and partially inhibits the utilization of co-ingested pyridoxine in humans. Journal of Nutrition. 127 1508-1513. 

Vitamin Bs consists of six forms in nature, i.e. pyridoxine (PN), pyridoxal (PL), pyridoxamine (PM), pyridoxine 5 -phosphate (PNP), pyridoxal 5 -phosphate (PLP), and pyridoxamine 5 -phosphate (PMP) (Figure 22.1). PLP is a coenzyme for many enzymes involved in amino acid and carbohydrate metabolism, and plays a key role in the nutritional function of vitamin Bg. The other forms show the same nutritional efficiency because they are converted into PLP in cells. The free forms of vitamin Bg are adsorbed through the intestinal mucosa, and then are phosphorylated and converted into PLP in the liver. Some PLP exits the liver and travels in the blood on albumin, being turned over slowly. PL is the form most actively transported to other cells from the liver. The cells adsorb PL and then phosphorylate it to yield PLP. The final metabolite derived from vitamin Bg is 4-pyridoxic acid (4-PA, Figure 22.1), which is excreted into the urine. Plants contain a storage form of vitamin Bg, pyridoxine-p-glucoside... 

Figure 22.1 Structures of natural vitamin Be forms, pyridoxine-P-glucoside, 4-pyr-idoxic acid and 4-pyridoxolactone.

Figure 22.2 Enzymatic reactions for specific conversion of vitamin Bg forms and pyridoxine-P-glucoside into 4-pyridoxolactone.

This chapter focuses on a determination method for all six vitamin Bg forms and pyridoxine-p-glucoside (PNG). 

Yagi, T., Murayama, R., Do, H.T.V., Ide, Y., Mugo, A.N., and Yoshikane, Y., 2010b. Development of a simultaneous enzymatic assay method for all six individual vitamin Bg forms and pyridoxine-p-glucoside. Journal of Nutritional Science and Vitaminology. 56 157-163. 

PMP) and pyridoxine-5 -phosphate (PNP) are also widely distributed in animal and plant tissues. Glycosylated forms of pyridoxine are commonly found in plants (8). The major glycosylated form of vitamin in plants is 5 -0-p-D glucopyra-nosyl pyridoxine (PN-glucoside) (8). The oxidized metabolites of pyridoxal, 3-hydroxy-5-hydroxymethyl-2-methylpyridine-4-carboxylic acid, and the corresponding lactone are designated 4-pyridoxic acid (4-PA) and 4-pyridoxolactone (4-PA lactone), respectively. 

JF Gregory, SL Ink. Identification and quantification of pyridoxine-beta-glucoside as a major form of vitamin Bg in plant-derived foods. J Agric Food Chem 35 76-82, 1987. 

Trumbo PR, Gregory JF, Sartain DB. Incomplete utilization of pyridoxine-beta-glucoside as vitamin B in the rat. J Nutr 118 170-175, 1988. 

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