Intrinsic factor receptor during fetal development of the human intestine.

Intrinsic factor receptor activity was observed in mucosal homogenates from whole small intestine and colon of 10-19-week fetuses, whereas it was only detected in the distal part of the small intestine of a 25-week fetus. The receptor-intrinsic factor-cobalamin complex was eluted into the void-volume position when ileum mucosal extract was assayed for receptor activity by gel filtration after incubation with either fetal gastric extract or human gastric juice. The intrinsic-factor-binding capacity of intestinal mucosal extracts ranged from 2.6 to 30.5 fmol/mg and was correlated with the gestational age of six fetuses. The dissociation constant of the receptor for the intrinsic factor-cobalamin complex was estimated at 0.24-0.36 nM at pH 7.4. In conclusion, intrinsic-factor-receptor activity was detected in the whole intestine in 10-19-week fetuses, whereas it was only present in the distal ileum at the end of fetal development.