Vitamin B-6 activity for rats of epsilon-pyridoxyllysine bound to dietary protein

The biological activity of protein bound epsilon-pyridoxyllysine residues in a phosphopyridoxyl-bovine serum albumin (PP-BSA) preparation was evaluated. Previous studies have demonstrated that pyridoxal phosphate may bind to food proteins as epsilon-pyridoxyllysine complexes during processing and storage. The present research, employing PP-BSA as a model, was initiated to determine the nutritional consequences of epsilon-pyridoxyllysine formation in foods. The concentration of epsilon-pyridoxyllysine residues in the PP-BSA was determined spectrophotometrically and chromatographically. Rat bioassay of the PP-BSA revealed that epsilon-pyridoxyllysine exhibited 60% activity relative to the molar potency of pyridoxine. These results suggest the partial release of bound vitamin B-6 possibly by in vivo enzymatic hydrolysis of epsilon-pyridoxyllysine. The presence of PP-BSA in a test diet containing 0.25 microgram added pyridoxine per g of diet inhibited the utilization of approximately half of the free pyridoxine by the rats. It is postulated that the observed inhibition resulted from an antivitamin B-6 effect of intact epsilon-pyridoxyllysine. This effect requires further investigation.