Association of pancreatic biotinidase activity and intestinal uptake of biotin and biocytin in hamster and rat.

Pancreatic biotinidase activity was higher in hamster than in rat; these results were reversed in plasma. Uptake was studied in everted intestinal rings. Saturation kinetics at 37 degrees C were observed for biotin in hamster and for biocytin in rat, with a Vmax of 1.83 and 1.05 nmol min-1 ml-1 and an apparent Kt of 25.14 and 40.7 microM, respectively. Biotin uptake by hamster intestine was reduced at 4 degrees C and when choline or potassium replaced sodium; it was inhibited by biocytin only at very high concentrations. Biocytin uptake in the rat was small compared to passive diffusion and was not influenced by sodium or temperature; it was not inhibited by biotin. We observed only passive diffusion of biotin in rat and of biocytin in hamster. Our results suggest that protein-bound biotin may be absorbed mainly in its free form in the hamster. In the rat, on the other hand, at least part of the dietary biotin may be absorbed lysine-bound, as biocytin.