Lactoferrin catabolism in the rat liver.
The hepatic uptake and degradation of human diferric 125I-lactoferrin by the liver of the intact rat were studied. After intravenous injection, the tracer was rapidly cleared by the liver, probably by adsorptive pinocytosis, as inferred from observations with a 3,470-fold dose range. Endocytosed lactoferrin was transferred, with a delay, from a light-density subcellular particle to an organelle that had a density similar to lysosomes. The loss of protein bound 125I from the liver was very slow (half-life 2.7 h), and its rate matched closely that of human asialotransferrin type 3. Lactoferrin was found to be a poor substrate for lysosomal hydrolases in vitro. Fucoidin effected the release of a portion of lactoferrin from the liver back into the plasma. By using this agent, indirect evidence was obtained suggesting that a fraction of lactoferrin is being repeatedly endo- and exocytosed (diacytosed) by the liver over prolonged periods of time. Fucosylation failed to impart lactoferrinlike properties on human asialotransferrin type 1, although the derivatized protein exhibited a less than or equal to 10-fold increase in affinity for the liver relative to the parent molecule.
D000818:Animals; D001692:Biological Transport; D005260:Female; D006801:Humans; D006867:Hydrolases / Q000378:metabolism; D007457:Iodine Radioisotopes; D007700:Kinetics; D007781:Lactoferrin / Q000378:metabolism*; D007782:Lactoglobulins / Q000378:metabolism*; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism; D008297:Male; D011134:Polysaccharides / Q000494:pharmacology; D051381:Rats; D013347:Subcellular Fractions / Q000378:metabolism; D014168:Transferrin / Q000378:metabolism
D007457:Iodine Radioisotopes; D007782:Lactoglobulins; D011134:Polysaccharides; D014168:Transferrin; C007789:fucoidan; D006867:Hydrolases; D007781:Lactoferrin