Determination of transferrin-like immunoreactivity in the mucosal homogenate of the duodenum, jejunum, and ileum of normal and iron deficient rats.

1. In intestinal mucosal tissue a transferrin-like immunoreactivity (TLIR) was determined after loading with 59Fe-(FeCl3) in vivo. The scraped-off mucosal tissue was homogenized and centrifuged at 100 000 X g. The supernatant was fractionated chromatographically. The TLIR was determined by the Mancini-test. 2. Extrapolated to infinite dilutions of the homogenate the following contents of the TLIR were calculated per cm of the intestinal segment: 28, 20, and 13, microgram/cm in the duodenum, jejunum, and ileum of iron-deficient animals and 15, 14, and 12 microgram/cm in the corresponding intestinal segments of normal rats, respectively. 3. The content of TLIR was compared with the iron uptake of the mucosal tissue from the intestinal lumen during absorption. An "iron turnover number" of 1.6 +/- 0.2 iron atoms per min during the absorption in duodenal and jejunal segments and of 0.5 +/- 0.1 in ileal segments of either iron-deficient and normal animals was calculated for the mucosal transferrin represented by the TLIR.