Attachment of the B12-Binding Principles Obtained from Lactobacillus leichmannii to Intestinal Mucosa Homogenates

Abstract

The B12-binding principles isolated from cellular components of Lacotobacillus leichmannii ATCC 7830 were studied for the activity to augment vitamin B12 uptake by intestinal mucosa homogenates (IMH) of the guinea pig, hog, rat, hamster, and man. It was found that the uptake of B12 by the IMH of these species was markedly augmented by these principles. The degrees of augmenta tion were much greater than that effected by the homologous intrinsic factor (IF). The IF-augmented uptake of B12 by guinea pig IMH was reduced when calcium ion was deleted from the incubation medium, while the deletion of calcium ion had no effect on the uptake augmented by the B12-binding principle. Boiling of IMH for 10min completely abolished the IF-augmented uptake of B12 but the effect of the B12-binding principle was not affected at all. These results indicate that difference exists between IF and the B12-binding principle in the mode of attachment to the adsorptive surface of the small intestine. The B12 uptake by everted sacs prepared from the distal portion of guinea pig ileum was slightly augmented by guinea pig IF but not by the B12-binding princinciple. However, the mucous materials liberated into the medium from the everted sacs during incubation took up large amounts of B12 in the presence of the B12 binding principle as well as IF.

Intestinal Mucosa and Vitamin B₁₂ Absorption

“…Human gastric juice contains, beside IF, the so-called 'R-binder', a non-IF-B12-binding protein which has a molecular weight of about 100.000 and is gel-filtered more rapidly than IF [29], A similar non-IF binder is present in crude hog IF preparations [33]. Sasaki [86] has recently purified B12 binders from the cell walls of lactobacilli that augment uptake of B12 by the mucosa or homogenates without need for Ca++ to a much greater extent than does IF. It seems desirable that some of the critical experiments in the past be repeated with pure human IF.…”