Proc. Nati. Acad. Sci. USA Vol. 75, No. 5, pp. 2215-2219 May 1978 Biochemistry Hepatic that specifically binds oligosaccharides containing fucosyl al- 3 N-acetylglucosamine linkages (fucose///lectin) JEAN-PAUL PRIEELS*, SALVATORE V. PIzzo, LOWRIE R. GLASGOW, JAMES C. PAULSON, AND ROBERT L. HILL Departments of Biochemistry and Pathology, Duke University Medical Center, Durham, North Carolina 27710 Contributed by Robert L. Hill, February 23, 1978

ABSTRACT Evidence is presented suggesting that hepa- Much is known about Lf structure although its biological role tocytes contain a receptor that binds specifically is obscure (8). Lf, like serotransferrin (Tf), has two -binding through fucose in al-..3 linkage to N-acetylglucosamine. sites, and iron binding is dependent on Its lactoferrin, which contains this type of linkage, is rap- (9). idly cleared from the circulation of mice after intravenous in- amino acid sequence is homologous with that of Tf (10, 11) and jection, and greater than 90% of the injected material is found ovotransferrin (11) and it contains two oligosaccharide chains, in . Binding of lactoferrin is mediated through its which are structurally similar to those of serotransferrin (Fig. carbhydrate groups, since its clearance is prolonged after 1), except that additional fucose residues are in a1->3 linkage periodate oxidation or after its oligosaccharide groups are ex- with the N-acetylglucosamine residues adjacent to galactose tensively degraded with glycosidases. In addition, gcopeptides from lactoferrin inhibit lactoferrin clearance. That lactoferrin and those chains containing fucose are devoid of sialic acid (11, clearance is mediated through binding to its fucosyl groups is 12, and unpublished observations). Although the studies re- suggested for several reasons. First, and asialo- ported here may reveal unknown aspects of Lf function, it is transferrin, whose oligosaccharide groups are essentially likely that the existence of a fucose-specific receptor in liver is structurally identical to those of lactoferrin but devoid of fucose, not limited in its function to binding only Lf. are not cleared on intravenous injection. Second, when fucose is incorporated into asialotransferrin by al-3 N-acetylgluco- MATERIALS AND METHODS samine fucosyl transferase, the resulting fucosylated derivative is cleared rapidly. Neither mannan nor derivatives of oroso- Human (13) and bovine Lf (14) were purified to homogeneity mucoid that are cleared by binding to receptors for galactose, by published procedures. Human Tf (homogeneous on sodium N-acetylglucosamine, or mannose, inhibit clearance of lacto- dodecyl sulfate gel electrophoresis; molecular weight 77,000) ferrin although clearance is inhibited by fucoidin. Finally, was from Sigma. Human was purified as de- glycoproteins containing fucose in al - 2 linkage to galactose scribed for the or al - 6 linkage to N-acetylglucosamine do not inhibit lac- bovine enzyme (15). Human was obtained toferrin clearance by the liver. Since clearance of other glyco- from the lactarium of the Oeuvre Nationale de l'enfance, , such as human lactoperoxidase, also appears to be Brussels, Belgium. (al-acid glycoprotein) was a mediated through binding to the same receptor as homogeneous preparation kindly supplied by Karl Schmid, lactoferrin, it is concluded tha the fucose-specific receptor Boston University. Human IgG and IgM were generous gifts studied here may fulfill other functions than binding lactoferrin. from C. D. Buckley, III (Duke University) and Frank Putnam Preliminary studies with liver homogenates and detergent ex- tracts of liver show binding in vitro. (University of Indiana, Bloomington), respectively. Porcine submaxillary and asialomucin were prepared as de- After the initial observations of Ashwell and coworkers (1, 2) scribed earlier (16). Commercial preparations of fucoidin that mammalian hepatocytes contain a that specifically (K & K Chem. Co.) and mannan (Sigma) were used without binds through exposed galactose residues, further characterization. GDPfucose al-o3 N-acetylglucosa- several other animal binding proteins were reported. A (3- mine fucosyltransferase was prepared from human milk (17, galactoside binding protein has been described from calf heart 18) and had a specific activity of 0.4 Amol of fucose transferred and lung (3), chick embryo thigh muscle (4), and the electric to lactose/min per mg of enzyme. GDP[14C]fucose (New En- organ of Electrophorus electricus (5), but they have properties gland Nuclear) was used in conjunction with that synthesized that differ somewhat from the hepatocyte protein and perhaps by published methods (19). Neuraminidase, ,314 galacto- from one another. Avian liver also contains a protein that binds sidase, fl-N-acetylglucosaminidase, and endo-fl-N-acetylglu- glycoproteins with exposed N-acetylglucosamine (6), and cosaminidase D were purified from Streptococcus pneumoniae considerable evidence has been reported for mannose-specific as described earlier (16). A partially purified mixture of gly- binding proteins (7). cosidases containing neuraminidase, fucosidase, fl-galactosidase, This report provides evidence suggesting the presence of a endo-(3-N-acetylglucosaminidase, and fl-N-acetylhexosamin- receptor in hepatocytes that specifically binds oligosaccharides idase were prepared from culture filtrates of Clostridium in glycoproteins through a fucosyl al- 3 N-acetylglucosamine perfringens.t C. perfringens neuraminidase was prepared as group. These studies were prompted by the observations that reported earlier (16). human lactoferrin (Lf) was rapidly cleared from the circulation Abbreviations: Lf, lactoferrin; 125I-Lf, radioactive iodinated lactoferrin; when injected intravenously in rats and mice, and that over 90% Tf, transferrin. of the injected protein was recovered in hepatocytes. * Present address: Laboratoire de Chimie G6nerale I, Facult6 des Sciences, Universit6 Libre de Bruxelles, 50 Ave. F. D. Roosevelt, The costs of publication of this article were defrayed in part by the B-1050, Brussels, Belgium. payment of page charges. This article must therefore be hereby marked t This mixture of glycosidases was obtained from fractions that were "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate isolated during preparation of a-N-acetylgalactosaminidase (20) and this fact. fucosidase (16). 2215 Downloaded by guest on September 28, 2021 2216 Biochemistry: Prieels et al. Proc. Nati. Acad. Sci. USA 75 (1978)

NeuAco2-o 6 GaI1R3-"-4GlcNAc,31--a2Man 3Man,83I --4GlcNAc,3I -*4GIcNAc --Asn NeuAcox2-6Ga1 ,31-"o4GIc NAc,9I--.2Manadl

FIG. 1. Structure of the oligosaccharide groups in human transferrin. Human lactoferrin is reported to contain fucose linked al-3 to the N-acetylglucosaminyl residues adjacent to the galactose (11, 12), but each oligosaccharide group contains only about 1 fucose residue. The fu- cose-containing chains of Lf are devoid of sialic acid (unpublished observations).

Orosomucoid, partially deglycosylated orosomucoids, lac- per 100. g. Human Lf also had the following carbohydrates toferrin, lactoperoxidase, and transferrin were labeled with 125I (residues per molecule based on molecular weight of 79,000): (New England Nuclear) as described earlier for growth hor- sialic acid (1.8), galactose (4.0), N-acetylglucosamine (8.2), and mone (21) and had specific radioactivities between 2 and 10 mannose (not quantitated). ,uCi/,ug. Iodination did not degrade the Lf, as judged by gel Clearance studies in albino mice (CD-1, female, 9-12 weeks filtration and gel electrophoresis. Periodate oxidation of gly- old, Charles River Labs, North Wilmington, MA) were per- coproteins was performed by published methods (7). Lacto- formed by injection of radiolabeled derivatives in the tail vein ferrin were isolated from Pronase digests and (10-500 ,l); blood samples (25 Ml) were removed at intervals purified by chromatography in water, first on columns (4 X 150 in heparinized capillary tubes from the orbital venous plexus cm) of Sephadex G-25 (superfine; Pharmacia), second on col- (23), and 125I radioactivity was measured in a y counter. umns (2 X 120 cm) of Sephadex G-50 (fine; Pharmacia), and Hepatocytes and Kupffer cells were separated by published then on columns (0.5 X 4 cm) of carboxymethyl-Sephadex C-25 methods (24), but livers were perfused prior to cell fractionation (Pharmacia) equilibrated with 0.05 M sodium cacodylate (pH by the method of Seglen (25). Carbonyl iron was first injected, 6) and eluted with the same buffer. The glycopeptides con- followed by 125I-labeled Lf (125I-Lf). tained the following amino acids in a mole ratio relative to as- partic acid (1): glutamic acid (0.5), threonine (0.38), glycine RESULTS (0.15), and serine (0.11). Deglycosylation of orosomucoid (40 Lactoferrin injected intravenously into mice and rats is rapidly mg/ml) was performed for 72 hr at 370 in 0.02 M cacodylate cleared from the circulation, as shown in Fig. 2 for the 125I- buffer (pH 6) with 0.08 unit of neuraminidase (C. perfringens) labeled derivative (125I-Lf). Less than 10% of the 125I-Lf is in per ml to give asialo-orosomucoid, with 0.08 unit of neurami- the circulation 10 min after injection, and a large majority of nidase per ml and 0.025 unit of f1-'>4 galactosidase (S. pneu- the radioactivity injected was found in the liver. In rats killed moniae) per ml to give asialoagalacto-orosomucoid, and with 9 min after injection, 85% of the radioactivity was in the liver 0.08 unit of neuraminidase per ml, 0.025 unit of (31 4 and the remainder in blood (10%), the kidneys (3.6%), and the galactosidase per ml, and 0.33 unit of (-N-acetylglucosaiinidase spleen (0.9%). Ninety-eight percent of the radioactivity that (S. pneumoniae) per ml to give asialoagalactoahexosamino- is cleared by the liver is in hepatocytes, and only 1.3% is in orosomucoid. The glycosidases were removed from degly- Kupffer cells (Table 1). cosylated glycoproteins by affinity adsorbents (16) or by heating Considerable evidence has been obtained to suggest that the at 80° for 15 min for the C. perfringens enzymes. Lf was also clearance of Lf by hepatocytes is mediated by specific inter- deglycosylated with S. pneumoniae glycosidases in addition action with the asparaginyl-linked oligosaccharide groups of to 0.08 unit of endo-f,-N-acetylglucosaminidase D per ml to Lf. First, clearance of 125I-Lf is inhibited by Lf, reduced and remove additional mannose, N-acetylglucosamine, and fucose. aminoethylated Lf, and the glycopeptides from Lf (Fig. 2). The glycosidases were removed by adsorption of Lf on car- Periodate-oxidized glycopeptides are much less effective in boxymethyl- under conditions (0.01 M sodium caco- inhibiting the clearance of 125I-Lf. Second, 125I-Lf oxidized with dylate, pH 6/0.1 M NaCl) that do not adsorb the enzymes. periodic acid and Lf enzymically deglycosylated with a mixture Asialotransferrin (0.86 mg/100 ,ul) was fucosylated by incu- of glycosidases from either S. pneumontae or C. perfringens bation with 80 nmol of GDP[14C]fucose (6290 cpm/nmol), 2.5 were not cleared as rapidly as 125I-Lf. ,umol of morpholinopropane sulfonate (pH 7.5), 2 ,umol of Lf clearance does not appear to involve those proteins in liver MnCl2, 0.02 unit of fucosyl transferase, and 1 mg of bovine that are specific for binding glycoproteins containing galactose, . The reaction was allowed to proceed at 370 for N-acetylglucosamine, or mannose at the nonreducing termini 19 hr; 0.02 unit of fucosyl transferase, 80 nmol of GDP[14C]- of their oligosaccharide groups. As shown in Fig. 3, Lf clearance fucose, and 1 mg of bovine in a final volume of 60 ,l were added at 4 and 9 hr. The product was isolated by gel Table 1. Cellular localization of 1251-Lf in rat liver filtration on a column (0.7 X 13 cm) of Sephadex G-50 (Phar- in 2.5 sul- Contam- Cellular content macia, fine) equilibrated mM morpholinopropane ination by Of 1251-Lf, fonate, pH 7.5/25 mM sodium chloride, followed by passage Yield other cell % of injected through two columns (0.4 X 5 cm) of DEAE-Sepharose (Phar- Cell type cells/g liver type, % sample macia) equilibrated in the same buffer in order to absorb and remove . The fucosylated derivative of Hepato- asialotransferrin contained 4.0 mol of fucose per mol of Tf. cytes 55 X 106 4 98 The fucose content (22) of the proteins and were as Kupffer follows (residues per molecule): human Lf (2.6), Lf degraded cells 11 X 106 0.02 1.3 extensively with S. pneumoniae glycosidases (1.3) or C. per- 125I-Lf (20 Itg; 10 Ci/g) was injected intravenously and hepatocytes fringens glycosidases (1.1), human Tf (<0.2), bovine Lf (0.6), and Kupffer cells were isolated (24) after perfusion of the livers with human lactoperoxidase (1.2), human IgG (0.75), and human . The cells were separated 25 min after injection of l25I-Lf. IgM (0.35). Porcine asialomucin contained 53 mmol of fucose Endothelial cells were not separated from Kupffer cells. Downloaded by guest on September 28, 2021 Biochemistry: Prieels et al. Proc. Natl. Acad. Sci. USA 75 (1978) 2217

60

0 10 20 30 0 10 20 30 Time, min Time, min FIG. 2. Clearance from blood of intravenously injected Lf under various conditions. 125I-Lf (1 sg, 2-10 Ci/g) or one of its chemically or en- zymically modified derivatives, was injected into mice, in some cases along with unlabeled Lf or a Lf derivative. Blood samples were collected at intervals and radioactivity was measured. (Left) 125I-Lf (0); 5I-Lf + Lf (4-10 mg) (A); 125I-Lfoxidized with periodic acid (0); 125I-Lfextensively degraded with glycosidases from S. pneumoniae (0) or C. perfringens (A). (Right) 125I-Lf (0); 125I-Lf + reduced and aminoethylated Lf (A); 125-Lf + Lf glycopeptides (A&); 125I-Lf + periodate-treated glycopeptides (0). Nephrectomized mice were used in and 0, but control studies with non-nephrectomized mice gave substantially the same results with the glycopeptides. is not inhibited by asialo-orosomucoid, asialoagalacto-oroso- groups of lactoferrin is fucose in al -3 linkage with N- mucoid, or asialoagalactoahexosamino-orosomucoid, which acetylglucosamine (Fig. 1), studies were performed to deter- terminate predominantly in galactose, N-acetylglucosamine, mine whether this linkage was required for Lf clearance. In and mannose, respectively. In addition, the clearance of each support of this view is the observation that fucoidin, which of the l25I-labeled orosomucoids is not inhibited by Lf, although contains some al-"3 linked fucose (26), prolonged the clear- their clearance is inhibited specifically by the homologous ance of 125I-Lf, although mannans, which inhibit clearance of orosomucoid derivative (data not shown). glycoproteins terminating in mannose (7) had little effect (Fig. Since a unique structural feature of the oligosaccharide 3). More conclusive evidence implicating fucose in the clear-

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L 0 10 20 30 0 10 20 30 Time, min Time, min FIG. 3. Clearance from blood of intravenously injected Lf and Tf under various conditions. All 125I-labeled proteins injected (1 Ag) were 2-10 Ci/g. Clearance was measured as described in Fig. 2. (Left) 125I Lf + 0.7 mg offucoidin (A), + 2 mg ofmannan (o), + 3 mg ofasialo-oroso- mucoid (A), + 2 mg of asialoagalacto-orosomucoid (-), + 1.8 mg of asialoagalactoahexosamino-orosomucoid (0). (Right) Human l25I-Tf (3), human 1251-asialo-Tf (0), human fucosylated l25I-asialo-Tf (0), human fucosylated l25I-asialo-Tf + 1.5 mg of human lactoferrin (v). Downloaded by guest on September 28, 2021 2218 Biochemistry: Prieels et al. Proc. Natl. Acad. Sci. USA 75 (1978)

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0 10 20 30 0 10 20 30 Time, min Time, min FIG. 4. Clearance from blood of intravenously injected human 4f, bovine Lf, and human lactoperoxidase under various conditions. Clearance was measured as described in Fig. 2. (Left) 125I-Lactoperoxidase (0), periodate-treated 125I-lactoperoxidase (0), 125I-Lf + 6 mg of lactoperoxidase CO), 125I-lactoperoxidase + Lf glycopeptides (-&). (Right) 125I-lLr. + 3.3 mg of bovine Lf (^,+0.7 mg of asialomucin (-), + 2.8 mg of human IgM (0), + 6 mg of human IgG () ance of Lf was obtained with studies on Tf and asialo-Tf, which 125I-Lf into mice revealed one radioactive peak at the void are not cleared rapidly on intravenous injection (Fig. 3). Tf volume, whereas Lf itself was retained under the same condi- oligosaccharides are devoid of fucose and contain two residues tions. This suggests that binding of Lf is mediated by a macro- of sialic acid per chain (Fig. 1); otherwise they are identical to molecular species, most likely a protein, but further knowledge those of Lf. Thus, if fucose is involved in clearance of Lf, Tf with of the properties of the binding protein awaits its purification fucose incorporated into al- 3 linkage into its N-acetylglu- and characterization. cosamninyl groups should be cleared. This was the case, as shown in Fig. 3, since asialo-Tf that was fucosylated with GDP[14C]- DISCUSSION fucose and GDPfucose al-3 N-acetylglucosaminyl fucosyl- transferase was cleared more rapidly than asialo-Tf itself. The data reported here support the view that Lf clearance from Moreover, clearance of the fucosylated transferrin was inhibited the circulation is dependent on its oligosaccharide groups rather by Lf (Fig. 3). The fucosylated asialo-Tf is not cleared by the than constituents in its polypeptide chain. Periodate oxidation hepatic galactoside receptors (1), since it did not bind with the or extensive enzymic deglycosylation prolongs its clearance. pure galactoside binding protein (data not shown). Clearance is also inhibited by glycopeptides from Lf, but per- Few glycoproteins containing the fucosyl a-1-3 N-acetyl- iodate-treated glycopeptides do not inhibit as extensively. Other glucosamine linkage are known; however, human milk lacto- data support the view that clearance is mediated specifically peroxidase, which has a fucose-containing oligosaccharide by binding to hepatocytes through fucose in al1-3 linkage to group, was also cleared rapidly (Fig. 4). In addition, its clear- N-acetylglucosamine in the oligosaccharide groups. Binding ance was prolonged after periodate oxidation and was inhibited proteins that are specific for galactose, N-acetylglucosamine, by glycopeptides from Lf. Moreover, the clearance of 125I-Lf or mannose do not appear to be involved since Lf clearance is was markedly inhibited by lactoperoxidase (Fig. 4). Fig. 4 also not inhibited by partially deglycosylated orosomucoid deriv- shows that 125I-Lf clearance is not inhibited by either human atives that are cleared by the three different binding proteins. IgG or IgM, which contain fucose in al- 6 linkage to N- Also, fucoidin, but not mannan, prolongs Lf clearance. Most acetylglucosamnine (27), or by porcine submaxiflary asialomucin, significant, however, is that human Tf, which has two oligo- which contains fucose in al-"2 linkage to galactose (27). Also, saccharide groups per molecule that are structurally similar to since bovine Lf inhibited the clearance of human l2I-Lf, which those of Lf but is devoid of fucose, is not cleared until fucose is was used throughout these studies, it is likely that bovine Lf also enzymically incorporated into its oligosaccharides. In addition, contains fucosyl al-*3 N-acetylglucosamine groups. These the clearance of fucosylated asialo-Tf is inhibited by Lf. Pure observations suggest that other glycoproteins with oligosac- fucosidases that will specifically remove fucose from Lf are charide groups similar to those of Lf and lactoperoxidase will presently unavailable, and it is impossible to test whether Lf be cleared by the same means as these two glycoproteins and clearance is prolonged when only its fucose is removed, but Lf that clearance is specific for one type of fucose linkage in oli- treated with mixtures of glycosidases that extensively degrade gosaccharides. its oligosaccharides and remove fucose is not cleared as rapidly Preliminary studies have revealed 125I-Lf binding to insoluble as Lf. microsomal preparations of mouse liver homogenates, and Although the clearance specificity has not been extensively binding is inhibited by Lf. Moreover, gel filtration (Ultragel examined, noteworthy is the observation that Lf clearance is RC34) of Triton X-100 extracts of homogenates prepared from not inhibited by either porcine asialomucin, which contains livers obtained 10 min after intravenous injection of 1 ,ug of fucose in a1-w2 linkage to galactose (27), or human IgG and Downloaded by guest on September 28, 2021 Biochemistry: Prieels et al. Proc. Natl. Acad. Sci. USA 75 (1978) 2219

IgM, which contain fucose in al-l-6 linkage to N-acetylglu- 1. Ashwell, G. & Morell, A. G. (1974) Adv. Enzymol. 41,99-128. cosamine (27). Thus, although clearance is dependent on fucose 2. Kawasaki, T. & Ashwell, G. (1976) J. Biol. Chem. 251, 5292- in the oligosaccharide, its location and its glycosidic linkage 5299. appear to be very critical. 3. DeWaard, A., Hickman, S. & Kornfeld, S. (1976) J. Biol. Chem. The nature of the enzymically fucosylated Tf used in these 251,7581-7587. 4. Den, H. & Malinzak, D. A. (1977) J. Biol. Chem. 252, 5444- studies requires special comment. Unpublished studies reveal 5448. that native Tf with its full complement of sialic acid (Fig. 1) is 5. Teichberg, V., Silman, I., Beitsch, D. D. & Resheff, G. (1975) not an acceptor for the al-'3 N-acetylglucosamine fucosyl- Proc. Nati. Acad. Sci. USA 72, 1383-1387. transferase, but that asialo-Tf is an excellent acceptor. Four 6. Kawasaki, T. & Ashwell, G. (1977) J. Biol. Chem. 252, 6536- residues of fucose per molecule are readily incorporated by 6543. the transferase into asialo-Tf, which is equal to one fucose res- 7. Kaplan, A., Achord, D. T. & Sly, W. S. (1977) Proc. Natl. Acad. idue per N-acetylglucosamine residue in the sequence Sci. USA 74,2026-2030. Gal#1-",4GlcNAcfl1-' 2Man. The resulting product contains 8. Arnold, R. R., Cole, M. F. & McGhee, J. R. (1977) Science 197, <0.04% of the fucose incorporated in al-'o2 linkage with ga- 263-265. lactose, as judged by its inability to serve as an acceptor for the 9. Aisen, P. & Liebman, A. (1972) Biochim. Blophys. Acta 257, A 314-323. blood-group-specific N-acetylgalactosaminyltransferase (28). 10. MacGillivray, R. T. A., Mendez, E. & Brew, 4. (1977) in Proteins In addition, the fucosylated asialo-Tf is not an acceptor for the in Iron Metabolism, eds. Brown, E. B., Aisen, P., Fielding, J. & f3-D-galactoside sialyltransferase (29), nor will it bind the pu- Crichton, R. C. (Grune and Stratton, New York), pp. 133-141. rified rabbit liver lectin of Ashwell and Morell (1). Thus, sialic 11. Spik, G. & Mazurier, J. (1977) in Proteins of Iron Metabolism, acid linked a2--6 to galactose prevents fucosylation, and fucose eds. Brown, E. B., Aisen, P., Fielding, J. & Crichton, R. C. (Grune linked al-"3 to N-acetylglucosamine prevents sialylation. and Stratton, New York), pp. 143-151. These studies will be reported in detail elsewhere, but they not 12. Dorland, L., Haverkamp, J., Schut, B. L., Vliegenthart, J. F. G., only illustrate the reciprocal action of fucosyl and sialyl trans- Spik, G., Strecker, G., Fournet, B. & Montreuil, J. (1977) FEBS ferases in oligosaccharide biosynthesis, but also the critical Lett. 77, 15-20. of the 13. Querinjean, P., Masson, P. L. & Heremans, J. F. (1971) Eur. J. nature location and linkage of fucose for clearance of Blochem. 20,420-425. fucose containing glycoproteins by liver receptors. 14. Castellino, F. J., Fish, W. W. & Mann, K. G. (1970) J. BPol. Chem. The biological significance of hepatocyte-binding proteins, 245,4269-4275. which are analogous to the plant lectins, remains obscure al- 15. Groves, M. L. & Kiddy, C. A. (1964) cited by Groves, M. L. (1971) though some may serve in the regulation of mammalian plasma in The Milk Proteins, ed. McKenzie, H. A. (Academic, New glycoprotein homeostasis, as suggested earlier (1). This may not York), Vol. II, p. 388. be the case for the fucose-specific lectin, since fucose is always 16. Glasgow, L. R., Paulson, J. C. & Hill, R. L. (1977) J. Blol. Chem. terminal in mammalian glycoproteins and the al-o3 fucosidic 252,8615-8623. linkage to N-acetylglucosamine has not been reported to be 17. Beyer, T. A., Prieels, J. P. & Hill, R. L. (1978) Fourth Interna- present in many plasma proteins (27). Nevertheless, the present tional Symposium on , in press. 18. Prieels, J. P., Beyer, T. A. & Hill, R. L. (1977) Biochem. Soc. studies indicate a biological role for fucose not evident here- Trans. 5, 838-839. tofore, and that this function is widely distributed in mammals, 19. Schachter, H., Hanako, I. & Heath, E. C. (1972) in Methods in since rabbits, as well as mice and rats, rapidly clear intrave- Enzymology, ed. Ginsberg, V. (Academic, New York), Vol. 28, nously injected Lf via the liver. It could be speculated that the pp. 285-287. fucose-lectin in hepatocytes is involved in some as yet unknown 20. Hill, H. D., Jr., Reynolds, J. A. & Hill, R. L. (1977) J. Blol. Chem. way in iron metabolism, but whether or not this is the case, the 252,3791-3798. fucose-lectin may serve other functions in view of its ability to 21. Greenwood, F. C., Hunter, W. M. & Glover, J. S. (1963) Biochem. clear lactoperoxidase and other proteins which appear to con- J. 89, 114-123. tain fucose in al -3 linkage to N-acetylglucosamine. Whatever 22. Spiro, R. G. (1966) in Methods in Enzymology, eds. Neufeld, E. functions the animal lectins fulfill, their presence in animal cells F. & Ginsberg, V. (Academic, New York), Vol. 8, pp. 3-26. along with the great of 23. Chase, M. W. (1967) in Methods in Immunology and Immu- diversity oligosaccharide structures with nochemistry, eds. Williams, C. A. & Chase, M. W. (Academic, the potential for specifying considerable molecular information New York), Chap. 2, Sect. D, Vol. I, pp. 252-306. suggests that other animal lectins, presently unknown, will be 24. Wincek, T. J., Hupka, A. L. & Sweat, F. W. (1975) J. Biol. Chem. discovered and that they could play vital roles in a variety of 250,8863-8873. intra- and intercellular processes. 25. Seglen, P. 0. (1973) Exp. Cell Res. 82, 391-398. 26. Percivol, E. (1970) in The Carbohydrates, eds. Pigman, W. & We thank Dr. Gilbert Ashwell (National Institures of Arthritis, Horton, D. (Academic, New York), Vol. IIB, 2nd Ed., pp. Metabolism, and Digestive Diseases, National Institutes of Health) for 537-568. reviewing this manuscript prior to submission for publication. This 27. Kornfeld, R. & Kornfeld, S. (1976) Annu. Rev. Biochem. 45, investigation was supported by Research Grant HL-06400 from the 217-237. National Heart and Lung Institute, National Institutes of Health. J.P.P. 28. Schwyzer, M. & Hill, R. L. (1977) J. Biol. Chem. 252, 2346- was the recipient of a NATO travel award; L.R.G. is a postdoctoral 2355. research trainee, National Institutes of Arthritis, Metabolism, and 29. Paulson, J. C., Rearick, J. I. & Hill, R. L. (1977) J. Bilo. Chem. Digestive Diseases, National Institutes of Health. 252,2363-2371. Downloaded by guest on September 28, 2021