Effects of epsilon-pyridoxyllysine bound to dietary protein on the vitamin B-6 status of rats.

The nutritional properties of protein bound epsilon-pyridoxyllysine residues in a phosphopyridoxyl bovine serum albumin (PP-BSA) preparation were examined by rat bioassay employing various levels of PP-BSA and pyridoxine (PN) fortification in the diets. Previous studies have shown that vitamin B-6 aldehydes can reductively bind to food proteins as epsilon-pyridoxyllysine complexes during processing and storage. The bound pyridoxyllysine was found to possess 50% molar vitamin B-6 activity, as indicated by slope ratios for rat growth, feed efficiency and liver pyridoxal 5'-phosphate concentration. The response curves indicated that high dosages of epsilon-pyridoxyllysine would fully satisfy the vitamin B-6 requirement. Direct antivitamin B-6 activity of epsilon-pyridoxyllysine was observed in diets containing low levels of PP-BSA. Classical rat acrodynia symptoms, depression of erythrocyte aspartate aminotransferase (AspAT) activity and elevation of in vitro coenzyme stimulation of AspAT were observed to be inversely related to PP-BSA concentration in the diet. The antivitamin B-6 effects were readily prevented by the presence of added 0.5--1.0 micrograms pyridoxing/g diet. In contrast to the previous study, the presence of PP-BSA in the diet did not inhibit the utilization of added PN. This difference was postulated to be due to a difference in vitamin B-6 concentration of the basal diets. The results of this study indicate that protein bound epsilon-pyridoxyllysine is nutritionally significant, presumably by its participation in the normal metabolism of vitamin B-6. The metabolic implications are discussed.