Hb J-Cordoba [alpha 2A beta 2(95)(FG2)Lys----Met]. A new Hb variant found in Argentina.

Hb J-Cordoba [alpha 2A beta 2(95)(FG2)Lys----Met], is one of the few hemoglobin variants discovered in Argentina. The structure and functional abnormalities are described. Hb J-Cordoba exhibits a slightly increased oxygen affinity, low cooperativity, and normal interaction with heterotropic cofactors.

Particle-counting immunoassay of human somatotropin.

Human somatotropin was assayed by a novel automated nonradioisotopic technique, "particle-counting immunoassay," that requires a 45-min incubation and only 60 microL of 10-fold diluted sample. The principle of the assay is agglutination of antibody-coated latex particle by somatotropin, the reaction being measured by the (instrumented) counting of residual non-agglutinated particles. The dynamic range in serum extends from 0.2 to 40 micrograms/L. The between-assay CV was 12% for a concentration of 3.3 micrograms/L and 8.5% for 31.9 micrograms/L. The coefficient of correlation (r) with radioimmunoassay was 0.97. Curves for various dilutions of the macromolecular and monomeric forms of the hormone were not parallel.

Uptake of lactoferrin by the liver. II. Endocytosis by sinusoidal cells.

Because of the controversy on the cell type involved in lactoferrin (Lf) uptake by the liver we localized injected Lf by immunofluorescence, light microscopic autoradiography, and light and electron microscope cytochemistry with Lf-peroxidase conjugates. These conjugates were essentially taken up by their Lf moiety as shown by competition experiments. By any procedure, Lf was almost exclusively found in the sinusoidal cells as well as in the wall of the central veins. These data directly demonstrate that both endothelial and Kupffer cells are responsible for Lf uptake by the liver.

Uptake of lactoferrin by the liver. III. Critical role of the protein moiety.

Three possible modes of recognition of human lactoferrin (Lf), which is avidly taken up by the mouse liver, were examined. First, Lf has terminal galactosyl residues for which a receptor exists on hepatocytes. However, when large amounts of Lf were injected with 125I-asialoorosomucoid, no inhibition of asialoorosomucoid uptake by the liver was observed. Second, Lf that exposes fucosyl residues could be recognized by the sugar-polyspecific receptor of liver sinusoidal cells. Digestion of Lf by fucosidase did not affect considerably the uptake of Lf. In addition, bovine Lf, which lacks fucosyl residues, was also avidly taken up by the liver, and this uptake was inhibited by human Lf. Mannan and horseradish peroxidase, which are recognized by the sugar-polyspecific receptor, did not inhibit Lf uptake. These data demonstrate that galactosyl and fucosyl residues are not essential for Lf recognition. Third, Lf could be recognized by its protein moiety. To investigate this possibility, we used two Lf derivatives with intact carbohydrate side chains, carbamylated Lf and the C-terminal half molecule of Lf. Carbamylation reduced the uptake of Lf and its competitive activity toward the uptake of 125I-Lf. The C-terminal fragment, like carbamylated Lf, had a much weaker competitive activity than intact Lf. Therefore, the integrity of the protein moiety of Lf was required for its effective uptake by the liver. As Lf is a cationic protein, competition experiments were also done with lysozyme, another cationic protein which in the form of dimer is taken up by the liver reticuloendothelial system. The strong inhibition by dimerized lysozyme suggests that the liver reticuloendothelial system has common binding sites for certain cationic proteins, as recently shown for isolated macrophages.

Uptake of lactoferrin by the liver. I. Role of the reticuloendothelial system as indicated by blockade experiments.

When 125I-labeled human lactoferrin was injected intravenously into mice it was rapidly taken up by the liver, where 75% of the dose was recovered after 15 minutes. The inhibition curve with unlabeled lactoferrin showed that the fates of labeled and unlabeled protein were similar and that the uptake capacity was saturable by milligram quantities of protein per gram of liver, suggesting the existence of numerous specific binding sites. The presence of these sites on the reticuloendothelial system was indicated by the blocking effect of dextran sulfate and latex particles. Fucoidin (fucan sulfate), which is used in the study of receptors specific for fucose, was found to inhibit the uptake of goat red blood cells as well as lactoferrin. Therefore, the inhibition exerted by fucoidin on the uptake of lactoferrin could be mediated by blockade of the reticuloendothelial system and not necessarily by competition for fucose receptors. These data indicate that the report by others that lactoferrin was taken up by a fucosyl receptor on hepatocytes is incorrect. The competition curve obtained when mouse lactoferrin was injected with its human homologue indicated that both proteins reacted with the same binding sites. However, a significant part of mouse lactoferrin was found to be taken up by the kidneys. Hepatic and renal uptakes were both reduced by prior injection of dextran sulfate.