Non-sequence-specific antimalarial activity of oligodeoxynucleotides

The effects of exogenously applied oligodeoxynucleotides on Plasmodium falciparum proliferation was investigated. A fluorescence-activated cell sorter assay was employed to measure parasitemia after administration of either phosphodiester or phosphorothioate oligodeoxynucleotides. We report sequence-independent antimalarial activity preferentially with phosphorothioate congeners with IC50 values in the 1-2 microM range. Phosphorothioate oligodeoxynucleotides which were antisense, sense or nonsense to Plasmodium mRNA, as well as homopolymers (30-mers containing all A or T bases) were equally effective inhibitors of parasitemia. The antimalarial activity was dependent upon oligomer length, concentration, and time of addition to the cultures but was independent of the parasite strain tested. Four P. falciparum strains, including a multi-drug-resistant strain (MDR-K), a drug-sensitive strain (FCR-3), a erythrocyte membrane sialic acid-independent strain (7G8) and a strain isolated from a cerebral malaria patient (CM-87) were equally susceptible to treatment with a phosphorothioate oligomer. Inhibition of red cell invasion is primarily responsible for the observed decrease in proliferation as determined by a study of parasite maturation in the presence of a 30-mer nonsense phosphorothioate oligodeoxynucleotide.

A monoclonal antibody capable of blocking the binding of Pf200 (MSA-1) to human erythrocytes and inhibiting the invasion of Plasmodium falciparum merozoites into human erythrocytes

Glycophorin A is a major receptor on human erythrocytes for Plasmodium falciparum, the human malaria parasite. In this work, we have produced four glycophorin A-specific mAb: 2B10, 1E4, 3H12, and 3H2. 2B10 was mapped to the amino terminal region of glycophorin (amino acids 1-31), and its binding to erythrocytes was fully dependent on sialic acid residues. 3H2 bound to the region close to the cell membrane, and its binding to Wr (b-) erythrocytes was significantly decreased, compared with its binding to Wr (b+) erythrocytes. 1E4 and 3H12 recognized sites between those identified by 2B10 and 3H2. Pf200 (MSA-1) is a surface protein on the P. falciparum merozoite which has been shown to bind to erythrocytes. By reciprocal inhibition assays, 2B10 and MSA-1 could be shown to share the same determinant on erythrocytes. Using an in vitro assay, we have shown that 2B10 was the most efficient inhibitor of the invasion of human erythrocytes by P. falciparum merozoites. We conclude that the binding site for MSA-1 is primarily located on the amino terminal region, amino acids 1-31, of glycophorin A, and that 2B10 is valuable for additional study of the interactions between P. falciparum merozoites and human erythrocytes.

A monoclonal antibody capable of blocking the binding of Pf200 (MSA-1) to human erythrocytes and inhibiting the invasion of Plasmodium falciparum merozoites into human erythrocytes

Glycophorin A is a major receptor on human erythrocytes for Plasmodium falciparum, the human malaria parasite. In this work, we have produced four glycophorin A-specific mAb: 2B10, 1E4, 3H12, and 3H2. 2B10 was mapped to the amino terminal region of glycophorin (amino acids 1-31), and its binding to erythrocytes was fully dependent on sialic acid residues. 3H2 bound to the region close to the cell membrane, and its binding to Wr (b-) erythrocytes was significantly decreased, compared with its binding to Wr (b+) erythrocytes. 1E4 and 3H12 recognized sites between those identified by 2B10 and 3H2. Pf200 (MSA-1) is a surface protein on the P. falciparum merozoite which has been shown to bind to erythrocytes. By reciprocal inhibition assays, 2B10 and MSA-1 could be shown to share the same determinant on erythrocytes. Using an in vitro assay, we have shown that 2B10 was the most efficient inhibitor of the invasion of human erythrocytes by P. falciparum merozoites. We conclude that the binding site for MSA-1 is primarily located on the amino terminal region, amino acids 1-31, of glycophorin A, and that 2B10 is valuable for additional study of the interactions between P. falciparum merozoites and human erythrocytes.

Molecular cloning and sequencing of a canine tracheobronchial mucin cDNA containing a cysteine-rich domain

To date the complete sequence of only one mammalian mucin cDNA, MUC1, has been reported, although several mucin proteins have been partially characterized. Here we report the nucleotide sequence of a canine tracheal mucin cDNA containing two potential translation initiation codons, one translation termination codon and a poly(A) tail. A lambda gt11 cDNA library prepared from canine tracheal epithelial cells was screened with polyclonal anti-apo-canine tracheal mucin antibodies with the aim of obtaining the deduced amino acid sequence of the mucin core protein. Antibody-positive clones containing overlapping inserts of various lengths were purified and used for nucleotide sequencing. Based on the sequencing data, synthetic oligonucleotide primers were constructed and both ends (5' and 3') of the cDNA were determined. The complete sequence was 3.7 kb and included an open reading frame with coding capacity for 1118 aa, two translation initiation ATG codons in context with Kozak consensus sequences, one polyadenylylation site, and a poly(A) stretch. The protein was rich in Thr, Pro, Ser, Gly, and Ala and poor in Tyr, Phe, and Trp. Although tandem repeats of amino acids were absent in the deduced canine tracheal mucin sequence, motifs TPTPTP and TTTTPV appeared 13 and 19 times, respectively. The C-terminal region contained a Cys-rich domain (although a few Cys residues were also present in the middle of the protein) as has been reported for bovine submaxillary mucin, porcine submaxillary mucin, rat intestinal mucin, human intestinal mucin, and frog skin mucin. This suggested that a broad group of mucins contain such a Cys-rich domain whose functional significance is yet to be understood. Three potential N-glycosylation sites were present in canine tracheal mucin and the amino acid sequence showed homology with both human tracheal and intestinal mucins. The N-terminal domain showed more flexibility (probably due to a high number of Pro residues in this region) when analyzed by the University of Wisconsin Genetics Computer Group program package to determine the predicted secondary structure. Evaluation of the transcripts using the canine mucin cDNA as a probe indicated a polydisperse message with total RNA.

Structural features of carbohydrate moieties in snake venom glycoproteins

The structures of the carbohydrate moieties of glycoproteins in snake venoms are largely unknown. In the present study, we have analyzed venoms of several species of snakes as well as plasma and tissue glycoproteins from one species of cobra (Naja naja kaouthia) by lectin affinity staining of Western blots. The data demonstrate that glycoproteins in cobra venom invariably contain terminal alpha-galactosyl residues with negligible proportions of sialic acids. Interestingly, however, terminal alpha-galactosyl residues are present in significantly lower proportions in cobra tissues such as brain, liver, lung, kidney, spleen, muscle, and totally absent in cobra plasma glycoproteins. In sharp contrast to cobras, venom glycoproteins of other snakes do not contain terminal alpha-galactosyl residues but do contain terminal 2,3- and/or 2,6-linked sialic acids as well as beta-galactosyl residues. Cobra venom also contains high molecular weight heavily glycosylated proteins bearing poly-N-acetyllactosaminyl oligosaccharides, the majority of which appear to be linked to the protein core via O-glycosidic bonds.

Cloning and cDNA sequence of a bovine submaxillary gland mucin-like protein containing two distinct domains

A lambda gt11 cDNA library prepared from bovine submaxillary gland mRNA was screened with polyclonal anti-apo-bovine submaxillary mucin antibodies with the aim of obtaining the deduced amino acid sequence of the mucin core protein. One of the positive clones had a 1.8 kilobase (kb) cDNA insert and coded for an incomplete protein. A 2.0-kb cDNA clone was isolated by rescreening the library with the 1.8-kb cDNA. Nucleotide sequencing of the full-length 2.0-kb cDNA revealed an open reading frame that coded for a 563-amino acid protein. A striking feature of the cloned protein is the skewed distribution of the amino acids, most notably that of the hydroxy amino acids and cysteine. The amino-terminal domain of 339 residues is very rich in threonine, serine, and glycine and poor in cysteine, aspartic acid, tyrosine, phenylalanine, and tryptophan. In contrast, the carboxyl-terminal domain of 224 residues is rich in cysteine, aspartic acid, tyrosine, lysine, and asparagine and relatively poor in threonine, serine, and glycine. A search of the protein data bank for homologies to the deduced amino acid sequence revealed statistically significant matches to several proteins, including the porcine submaxillary apomucin fragment. The cysteine-rich domain by itself was not statistically homologous with any of the registered polypeptide sequences. RNA blot analysis using DNA probes corresponding to the mucin-like and cysteine-rich regions detected a nearly identical pattern of transcripts, demonstrating that the characterized clones are not artifacts of cDNA library construction. The blots also showed the presence of polydisperse transcripts in bovine submaxillary gland but no detectable hybridization signals in liver or brain RNA.

Modification of sialyl residues of glycoconjugates by reductive amination. Characterization of the modified sialic acids

The sialic acid residues of alpha 1-acid glycoprotein and fetuin were modified by introduction of an amino residue, such as glycine and [3H]glycine. This modification involved (a) the selective periodate oxidation of the exocyclic carbon atoms of the sialic acid residue generating an aldehyde group at C-7, and (b) the reduction of the Schiff base formed with an amino compound by use of sodium cyanoborohydride. Thin layer chromatography, high pressure liquid chromatography, and amino acid composition data of the modified glycoprotein showed that the conversion was essentially quantitative. The glycine-modified sialic acids were isolated by mild acid hydrolysis and identified by g.l.c.-m.s. and n.m.r. spectroscopy, thus confirming that the quantitative modification produced a glycine-aminated C-7 sialic acid analog. Strong acid hydrolysis of the glycine-modified sialic acid yielded a fragment that had chromatographic characteristics similar to those of glycine.

Protein components of human tracheobronchial mucin: partial characterization of a closely associated 65-kilodalton protein

A high-density mucin glycoprotein was isolated from human tracheobronchial secretions substantially free of contaminating protein, low-density glycoprotein, proteolytic enzymes, and lipid. A closely associated 65-kDa protein was discovered while investigating the effect of 2-mercaptoethanol treatment on the purified mucin glycoprotein. It has been established that the 65-kDa protein is neither alpha 1-antichymotrypsin nor human serum albumin, two proteins of similar molecular weight which are found in crude tracheobronchial secretions. This protein lacks cross-reactivity with antibodies directed against serum components and is presumably comparable to the 65-kDa protein similarly isolated from canine tracheal pouch secretions [Ringler et al. (1987) Biochemistry 26, 5322-5328]. Although both the presence of sulfhydryl groups and the ability to be reassociated with the mucin molecule have been established, it is not clear whether its association is due to direct disulfide bonding, hydrophobicity, or entrapment. It was found that 14C-methylated methemoglobin was an inappropriate substrate for measurement of proteolytic activity in mucin preparations due to inherent entrapment and clearance capabilities of mucin molecules.

Purification and partial characterization of a malignancy-associated glycoprotein

The isolation from cancer patient serum of a glycoprotein (Cc) associated with the presence of a variety of malignancies was previously reported. Although preliminary chemical and physical data indicated that Cc was different from identified circulating glycoproteins, subsequent immunological studies suggested that it was closely related to alpha 1-acid glycoprotein. Further analysis revealed the presence of two components in some Cc preparations and prompted a re-examination of the isolation and characterization data. In the present study, Cc was purified by a modified protocol which involved the use of pleural fluid obtained from individuals with cancer, and an alpha 1-acid glycoprotein antibody column to remove contaminating alpha 1-acid glycoprotein. Typically, the material not retained by the antibody column gave a single band with Mr 53,000 when subjected to sodium dodecyl sulfate-polyacrylamide electrophoresis. Amino terminal analysis revealed that the protein contained a blocked amino terminus, and carbohydrate analysis indicated that complex, asparagine-linked saccharide units were present. The product could be distinguished from alpha 1-acid glycoprotein and other previously described circulating glycoproteins by several criteria, including molecular weight, isoelectric point, and amino acid and carbohydrate composition. One of three preparations isolated had an apparent Mr of 59,000. Carbohydrate analysis as well as deglycosylation studies showed that the change in molecular weight was due to increased glycosylation.

Ultrastructural localization of erythrocyte cytoskeletal and integral membrane proteins in Plasmodium falciparum-infected erythrocytes

The distributions of ankyrin, spectrin, band 3, and glycophorin A were examined in Plasmodium falciparum-infected erythrocytes by immunoelectron microscopy to determine whether movement of parasite proteins and membrane vesicles between the parasitophorous vacuole membrane and erythrocyte surface membrane involves internalization of host membrane skeleton proteins. Monospecific rabbit antisera to spectrin, band 3 and ankyrin and a mouse monoclonal antibody to glycophorin A reacted with these erythrocyte proteins in infected and uninfected human erythrocytes by immunoblotting. Cross-reacting malarial proteins were not detected. The rabbit sera also failed to immunoprecipitate [3H]isoleucine labeled malarial proteins from Triton X-100 and sodium dodecyl sulfate (SDS) extracts of infected erythrocytes. These three antibodies as well as the monoclonal antibody to glycophorin A bound to the membrane skeleton of infected and uninfected erythrocytes. The parasitophorous vacuole membrane was devoid of bound antibody, a result indicating that this membrane contains little, if any, of these host membrane proteins. With ring-, trophozoite- and schizont-infected erythrocytes, spectrin, band 3 and glycophorin A were absent from intracellular membranes including Maurer's clefts and other vesicles in the erythrocyte cytoplasm. In contrast, Maurer's clefts were specifically labeled by anti-ankyrin antibody. There was a slight, corresponding decrease in labeling of the membrane skeleton of infected erythrocytes. A second, morphologically distinct population of circular, vesicle-like membranes in the erythrocyte cytoplasm was not labeled with anti-ankyrin antibody. We conclude that membrane movement between the host erythrocyte surface membrane and parasitophorous vacuole membrane involves preferential sorting of ankyrin into a subpopulation of cytoplasmic membranes.

Deglycosylation studies on tracheal mucin glycoproteins

Following several model experiments, conditions were developed for optimal deglycosylation of tracheal mucin glycoproteins. Exposure of rigorously dried material to trifluoromethanesulfonic acid at 0 degree C for up to 8 h results in cleavage of essentially all fucose, galactose, and N-acetylglucosamine, about 80% of the N-acetylneuraminic acid (NeuNAc), and a variable amount of N-acetylgalactosamine (GalNAc), the sugar involved in linkage to protein. Residual N-acetylneuraminic acid is sialidase susceptible and apparently in disaccharide units, presumably NeuNAc2----GalNAc. The remaining N-acetylgalactosamine is mostly present as monosaccharides, and a few Gal beta 1----3GalNAc alpha units are also present; both are cleaved by appropriate enzymatic treatment. The saccharide-free proteins obtained from either human or canine mucin glycoproteins have molecular weights of about 100,000 and require chaotropic agents or detergents for effective solubilization.

Structure of canine tracheobronchial mucin glycoprotein

Canine tracheal mucin glycoprotein was isolated from beagle dogs fitted with tracheal pouches. Following exclusion chromatography on Sepharose CL-4B, noncovalently associated proteins were further resolved by dissociative density gradient centrifugation in CsBr-guanidinium chloride, and the mucin was then extracted with chloroform-methanol. The delipidated high-density product obtained had a nominal molecular weight of about 10(6) and an overall composition characteristic for a mucin glycoprotein, viz., a high content of serine and threonine, about 80% carbohydrate by weight, the absence of mannose or uronic acid, measurable ester sulfate, and a Pronase-resistant domain of molecular weight (1.75-3.0) X 10(5) which contains essentially all of the saccharide residues. Noncovalently bound lipid amounted to 6-10% by weight and was primarily cholesterol and cholesteryl esters. Cleavage of disulfide bonds by performic acid oxidation resulted in the release of a protein (Mr 65,000) not otherwise resolved by sodium dodecyl sulfate gel electrophoresis or the purification scheme.

Distinguishing between Nitrification and Denitrification as Sources of Gaseous Nitrogen Production in Soil

The source of N 2 O produced in soil is often uncertain because denitrification and nitrification can occur simultaneously in the same soil aggregate. A technique which exploits the differential sensitivity of these processes to C 2 H 2 inhibition is proposed for distinguishing among gaseous N losses from soils. Denitrification N 2 O was estimated from 24-h laboratory incubations in which nitrification was inhibited by 10-Pa C 2 H 2 . Nitrification N 2 O was estimated from the difference between N 2 O production under no C 2 H 2 and that determined for denitrification. Denitrification N 2 was estimated from the difference between N 2 O production under 10-kPa C 2 H 2 and that under 10 Pa. Laboratory estimates of N 2 O production were significantly correlated with in situ N 2 O diffusion measurements made during a 10-month period in two forested watersheds. Nitrous oxide production from nitrification was most important on well-drained sites of a disturbed watershed where ambient NO 3 − was high. In contrast, denitrification N 2 O was most important on poorly drained sites near the stream of the same watershed. Distinction between N 2 O production from nitrification and denitrification was corroborated by correlations between denitrification N 2 O and water-filled pore space and between nitrification N 2 O and ambient NO 3 − . This technique permits qualitative study of environmental parameters that regulate gaseous N losses via denitrification and nitrification.

Isolation and characterization of a wheat germ agglutinin-binding glycoprotein from B16 mouse melanoma cells

Cells of B16 mouse melanoma grown in serum-free medium in the presence of [3H]glucosamine secreted or shed labeled glycoproteins. A wheat germ agglutinin-binding glycoprotein was isolated that accounted for 37% of the total [3H]glucosamine incorporated; it had a molecular weight of approximately 50,000 and was absent in less-tumorgenic wheat germ agglutinin (isolectin I)-resistant variants of the cells. The glycoprotein contained approximately 25% of serine and threonine plus equimolar amounts of glucosamine and galactosamine, indicating both N- and O-linked oligosaccharide chains. Neuraminidase treatment released approximately 60% of the glycoprotein's 3H radioactivity as N-acetylneuraminic acid. The sialoglycoprotein did not, but the desialylated species did, bind (97%) to ricin-Sepharose, suggesting the presence of terminal sialic acid and penultimate galactose residues in most of the saccharide units. Alkaline borohydride released 61% of the glycoprotein's radioactivity as oligosaccharide alcohols that were mainly tetrasaccharides (75%) with some branched trisaccharides (10%) from the O-linked structures. Hydrazinolysis and analysis of the alkaline borohydride-resistant portion of the glycoprotein indicated the presence of mainly triantennary, complex-type structures (N-linked) containing three sialic acids residues plus L-fucose. Serial lectin-affinity chromatography of the hydrazine-released saccharides with concanavalin A-agarose, pea lectin-agarose, L-PHA-agarose, and E-PHA-agarose, indicated the absence of high-mannose or hybrid-type structures and further confirmed the presence of triantennary, complex-type units.

Characteristics of two wheat germ agglutinin-resistant variants of B16 mouse melanoma cells with reduced tumorigenicity

Two variants of B16 mouse melanoma cells, selected for their resistance to toxic levels of wheat germ agglutinin isolectin 1 (WGA-1) in serum-free medium, showed by chromosome analysis that they are still mouse cell-lines, continue to produce melanin, and are less tumorigenic in mice than the parent B16 cells. The variants showed a marked decrease in cell agglutination with the wheat germ lectin and a slight increase in cell agglutination with concanavalin A. The binding of 125I-labeled wheat germ agglutinin to the two variant lines was likewise decreased over a 10(3)-fold range of lectin concentrations. Terminal sialyl residues were critical in WGA-1 binding to the wild-type cells. The binding data indicated a decrease in high-affinity binding as well as a decrease in the total number of binding sites in the variants. Polyacrylamide gel electrophoresis, followed by affinity staining with 125I-wheat germ agglutinin, showed alterations in the wheat germ agglutinin-binding glycoproteins in the variants compared to those of the parent cell line. However, lactoperoxidase-catalyzed iodination revealed a similar cell-surface protein pattern among the three cell lines. Radioactive glycoproteins secreted or shed by the three cell lines grown in the presence of [3H]glucosamine in serum-free medium were fractionated on the basis of their interaction with WGA-Sepharose (2 mg/mL). The WGA-bound glycoproteins from the two variants had molecular weights of 92,000, 56,000, and 42,000. None of these components was detected in the parent cell-line. A major WGA-binding glycoprotein, which accounted for 37% of the total [3H]glucosamine incorporated, was isolated from the spent medium of the parent mouse melanoma cell-line. This glycoprotein was apparently absent in the WGA-1-resistant variants.

Isolation and characterization of proteoglycans secreted by normal and malignant human mammary epithelial cells

The proteoglycans secreted by a malignant human breast cell line (MDA-MB-231) were compared with the corresponding proteoglycans from a normal human breast cell line (HBL-100). The physicochemical characteristics of these proteoglycans were established by hexosamine analysis, chemical and enzymatic degradations, and dissociative cesium chloride density gradient centrifugation, and by gel filtration before and after alkaline beta-elimination. Both cell lines secreted approximately 70% of the synthesized proteoglycans, which were composed of 20% heparan sulfate and 80% chondroitin sulfate proteoglycans. The MDA cell line secreted large hydrodynamic size (major) and small hydrodynamic size heparan sulfate proteoglycan. In contrast HBL cells secreted only one species having a hydrodynamic size intermediate to the above two. The chondroitin sulfate proteoglycans from MDA medium were slightly larger than the corresponding polymers from HBL medium. All proteoglycans except the small hydrodynamic size heparan sulfate proteoglycan from MDA medium were of high buoyant density. The proteoglycans of both cell lines contained significant proportions of disulfide-linked lower molecular weight components which were more pronounced in the proteoheparan sulfate polymers, particularly those from MDA medium, than in chondroitin sulfate proteoglycans. The glycosaminoglycans of heparan sulfate proteoglycans from MDA medium were more heterogeneous than those from HBL medium. The glycosaminoglycan chains of large hydrodynamic size heparan sulfate proteoglycans from MDA medium were larger in size than those from HBL medium while small hydrodynamic size heparan sulfate proteoglycans contained shorter glycosaminoglycan chains. In contrast to the glycosaminoglycans derived from chondroitin sulfate proteoglycans of both MDA and HBL medium were comparable in size. The heparan sulfate as well as chondroitin sulfate proteoglycans of both cell lines contained both neutral (di- and tetrasaccharides) and sialylated (tri- to hexasaccharides) O-linked oligosaccharides.

Structures of O-linked oligosaccharides present in the proteoglycans secreted by human mammary epithelial cells

The structures of O-glycosidically linked oligosaccharides present in the heparan sulfate and chondroitin sulfate proteoglycans isolated from the culture medium of a normal (HBL-100) and a malignant (MDA-MB-231) human mammary epithelial cell line have been determined. Both proteoglycan types from the two cell lines contain a series of O-linked oligosaccharides ranging in size from di- to hexasaccharide. Cells were grown in the presence of either [3H]glucosamine or [3H]galactose and Na2 35SO4, and the proteoglycans were isolated as described (Gowda, D. C., Bhavanandan, V. P., and Davidson, E. A. (1986) J. Biol. Chem. 261, 4926-4934). The O-linked oligosaccharides were released from the proteoglycans by alkaline borohydride treatment and purified by a combination of gel filtration and high voltage paper electrophoresis. The structures of two neutral and seven acidic oligosaccharides were established based on sugar composition, the results of periodate oxidation, sequential exoglycosidase treatment, and methylation analysis. Periodate oxidation, taking advantage of tritium label at specific positions of constituent sugars, proved to be a valuable tool in establishing the structure of isomeric components in the mixture. The structures of the oligosaccharides were assigned as follows: (Formula: see text) The oligosaccharide containing both sialic acid and ester sulfate is novel and has not been reported previously.

Epitopes immunologically related to glycophorin A on human malignant and non-malignant cells in culture

Nine monoclonal antibodies specific to different antigenic determinants on the cyanogen bromide fragments CNBr3 (1-8) and CNBr1 (9-81) of glycophorin A, the major sialoglycoprotein of human red blood cells, were used for the detection of similar or cross-reactive epitope(s) on nucleated somatic cells. A panel of human malignant and non-malignant cells consisting of erythroleukemia, melanoma and carcinomas of breast, cervix, larynx, nasopharynx and colon, as well as human fibroblasts and mammary cells, were tested using a sensitive enzyme-linked immunoassay. The presence of glycophorin-like epitopes were demonstrated, in varying concentrations, on all cells tested. These epitropes were found to be localized on the cell membranes by indirect immunofluorescence.

Mucin and fat emboli in mucinous carcinomas. Cause of hemorrhagic cerebral infarcts

A patient with a mucin-producing carcinoma of the breast died after three weeks of progressive neurologic deterioration. At autopsy, numerous small hemorrhagic cerebral infarcts of varying ages were found. The infarcts were primarily located in arterial boundary zones of cerebral and cerebellar hemispheres. They were associated with numerous mucin and fat emboli. In any unexplained cerebral infarct in patients with mucin-producing carcinoma, mucin and fat emboli should be considered and searched for.

Radioimmunoassay of a glycoprotein associated with malignancy

A glycoprotein associated with malignancy was purified from the 0.6M perchloric acid-soluble fraction of serum obtained from cancer patients. The purified glycoprotein contained sialic acid, which was responsible for binding to wheat-germ agglutinin-Sepharose. Gel electrophoresis showed one band with an apparent Mr of 50 000-55 000, and the isoelectric point was 4.4 +/- 0.1. The glycoprotein could be distinguished from carcinoembryonic antigen and alpha-fetoprotein. Iodination of this material with chloramine-T permitted development of a radioimmunoassay.

Radioimmunoassay of a cancer-related glycoprotein. Circulating levels

Circulating levels of (a) tumor-related glycoprotein(s) were determined by radioimmunoassay for a variety of patients and controls, and correlated with sialic acid concentration. Levels were highest in patients with metastatic disease and progressively declined to those with localized disease receiving therapy. Values for normal, adjuvant, and cured patients were significantly lower. Sialic acid concentrations correlated best for the metastatic group but not for the normals.