Domain structure of proteoheparan sulphate from confluent cultures of human embryonic skin fibroblasts.

Radiolabelled proteoheparan sulphates were isolated from confluent monolayers of fibroblasts and from their spent media. The cell-surface-associated proteoglycan (Mr 350 000) has a core protein of Mr 180 000 that is cleaved by reduction of disulphide bonds into polypeptides of Mr 90 000, both of which can bind transferrin [Fransson, Carlstedt, Cöster & Malmström (1984) Proc. Natl. Acad. Sci. U.S.A. 81, 5657-5661]. Thrombin digestion of the proteoglycan yielded two major fragments. The larger one contained the heparan sulphate chains and glycoprotein-type oligosaccharides, whereas the smaller one contained interchain disulphide bond(s) and had affinity for transferrin as well as for octyl-Sepharose. The larger thrombic fragment was cleaved by trypsin into fragments containing the heparan sulphate chains and the oligosaccharides respectively. The smaller proteoheparan sulphate derived from the culture medium (Mr 150 000) had a core protein of Mr 30 000, which contained heparan sulphate-attachment and oligosaccharide-attachment regions, but no domains for binding of transferrin or for hydrophobic interactions.     

Bovine arterial smooth muscle cells synthesize two functionally different proteoheparan sulfate species

Cultured arterial smooth muscle cells synthesize two proteoheparan sulfate species. One is found associated with the cells, whereas the other is excreted into the medium. The two proteoheparan sulfates have similar hydrodynamic sizes but differ in the Mr of their core proteins. The cell-associated proteoheparan sulfate has a Mr of 92,000 while that of soluble proteoheparan sulfate is 38,000. The cell-associated and the soluble proteoheparan sulfate species differ in their ability to suppress the proliferation of smooth muscle cells. When added to the culture medium 2-5 micrograms/ml of the cell-associated and 20-25 micrograms/ml of the soluble proteoheparan sulfate species inhibit the growth of smooth muscle cells half maximally. The antiproliferative potency of both species resides in the heparan sulfate chains. Commercially available heparin has no antiproliferative effect and is not able to prevent the antiproliferative action of cellular heparan sulfate. In contrast to heparin, none of the heparan sulfate preparations has anticoagulant activity. Smooth muscle cells endocytose the soluble heparan sulfate at a rate three to four times higher than that of the cell-associated heparan sulfate. The data suggest that the cell-associated and the soluble proteoheparan sulfate species are separate and possibly genetically distinct molecules. Furthermore, the structural determinants for antiproliferative activity and the recognition sites for endocytotic uptake appear to be different.     

Cell-associated proteoheparan sulfate from bovine arterial smooth muscle cells

Cell-associated proteoheparan sulfate has been isolated from bovine arterial smooth muscle cells preincubated with [35S]sulfate or a combination of [3H]glucosamine and [35S]methionine. The purified proteoheparan sulfate had an apparent Mr of 200,000 on calibrated Sepharose CL-2B columns. The glycosaminoglycan component (Mr approximately 30,000) was identified as heparan sulfate by its susceptibility to specific enzymatic and chemical degradation. After degradation of the proteoheparan sulfate by microbial heparitinase the resulting protein core had an apparent Mr of 92,000 on SDS-polyacrylamide gels. Its mobility was similar in the absence and presence of reducing agents indicating that the protein core consists of a single polypeptide chain. Pulse-chase experiments revealed that about 40% of the cell layer-associated proteoheparan sulfate was released into the medium, while the remainder was internalized and converted to smaller species through a series of degradation steps. Initially there was a proteolytical cleavage of the protein core generating glycosaminoglycan peptide intermediates with polysaccharides chains similar in size to the original. The half-life of the native proteoheparan sulfate was found to be about 4 h.     

Detergent-solubilized proteoglycans in rat testicular Sertoli cells

Rat Sertoli cells were cultured for 48 h in the presence of [35S]sulfate and extracted with 4 M guanidine chloride. In this extract, a Sepharose CL-2B Kav 0.10 proteoheparan appeared lipid associated, since after addition of detergent it emerged at Kav = 0.65 on Sepharose CL-2B. Treatment of cells with 0.2% Triton X-100 released 35S-labeled material which was purified by ion-exchange chromatography and hydrophobic interaction chromatography on octyl-Sepharose. Proteoglycan with affinity for octyl-Sepharose (Kav = 0.30 and 0.12 on Sepharose CL-4B and CL-6B, respectively) mostly carried heparan sulfate chains with Kav = 0.38 and minor proportion of heparan chains with Kav = 0.77 on Sepharose CL-6B. An association with lipids was confirmed by intercalation into liposomes of this proteoheparan which might be anchored in the plasma membrane, via an hydrophobic segment and/or covalently linked to an inositol-containing phospholipid. Non-hydrophobic material consisted of: (i) proteoheparan slightly smaller in size than lipophilic proteoheparan and possibly deriving from this one and (ii) two heparan sulfate glycosaminoglycan populations (Kav = 0.38 and 0.86 on Sepharose CL-6B) corresponding to single glycosaminoglycan chains and their degradation products.     

Biochemical and ultrastructural studies of proteoheparan sulfates synthesized by PYS-2, a basement membrane-producing cell line

The mouse teratocarcinoma-derived cell line, PYS-2, has been shown to produce laminin, a basement membrane-specific glycoprotein. In these studies we demonstrate that PYS-2 cells synthesize and secrete into the culture medium a proteoglycan which contains only heparan sulfate as its sulfated polysaccharide side chains, as well as type IV procollagen and laminin. The apparent molecular weights of the proteoglycan and its heparan sulfate side chain were estimated to be 400,000 and 25,000, respectively, by gel chromatography. A proteoheparan sulfate with properties closely similar, if not identical, to those of the proteoglycan in the medium, together with two heparan sulfate single chains of different molecular size, were extracted from the cell layer with 2% SDS in the presence of protease inhibitors. Ultrastructurally, a fine fibrillar intercellular matrix was recognized which contained discrete 100-200 A diameter ruthenium red-positive granules interspersed throughout the filamentous meshwork. The PYS-2 cultures were shown by immunofluorescence to react with antibodies against the heparan sulfate-containing proteoglycan isolated from the mouse EHS sarcoma (Hassell, J. R., P. G. Robey, H. J. Barrach, J. Wilczek, S. I. Rennard, and G. R. Martin. 1980. Proc. Natl. Acad. Sci. U. S. A. 77:4494-4498). Immunoelectron microscopic examination, using the same antibodies, revealed that the proteoheparan sulfate was located not only at the edges but also within the interstices of the matrix. These findings indicate that PYS-2 cells synthesize and secrete a proteoglycan with properties similar to those of basement membrane proteoglycan. These cells may therefore serve as a useful model system for the study of the biosynthesis and structure of basement membranes.     

Isolation and characterization of two proteoheparan sulfate species of calf arterial tissue

When calf aortic tissue, preincubated under organ culture conditions in the presence of [35S]sulfate, was submitted to a sequential collagenase and elastase digestion and guanidinium chloride extraction, the bulk of proteoheparan sulfate was obtained in the elastase fraction. Ion-exchange chromatography on DEAE-cellulose of the elastase digest under dissociative conditions yielded a proteoglycan fraction that contained heparan sulfate as the sole glycosaminoglycan. The proteoheparan sulfate fraction was resolved into a high-molecular-mass (P-HS 1) and a low-molecular-mass (P-HS 2) fraction by gel filtration on Sephacryl S-400. P-HS 1 has a Mr of 175,000 and possesses four heparan sulfate side-chains (Mr 32,000) covalently bound to the protein core via a galactose- and xylose-containing polysaccharide-protein binding region. The protein core (Mr 38,000), which was obtained after deglycosylation of PG-HS 1 with trifluormethane sulfonic acid, contained in addition a few N-glycosidically linked oligosaccharide units representing a complex type with terminal neuraminic acid residues. P-HS 2 is a single-chain peptidoheparan sulfate of Mr of 38,000 containing one heparan sulfate chain (Mr 32,000) linked to a polypeptide (Mr 6000). The ratio of specific radioactivities of P-HS 1 and P-HS 2 was 1:0.66.     

Dithiothreitol activation of the insulin receptor/kinase does not involve subunit dissociation of the native alpha 2 beta 2 insulin receptor subunit complex

The subunit composition of the dithiothreitol- (DTT) activated insulin receptor/kinase was examined by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis and gel filtration chromatography under denaturing (0.1% SDS) or nondenaturing (0.1% Triton X-100) conditions. Pretreatment of 32P-labeled insulin receptors with 50 mM DTT followed by gel filtration chromatography in 0.1% SDS demonstrated the dissociation of the alpha 2 beta 2 insulin receptor complex (Mr 400,000) into the monomeric 95,000 beta subunit. In contrast, pretreatment of the insulin receptors with 1-50 mM DTT followed by gel filtration chromatography in 0.1% Triton X-100 resulted in no apparent alteration in mobility compared to the untreated insulin receptors. Resolution of this complex by nonreducing SDS-polyacrylamide gel electrophoresis and autoradiography demonstrated the existence of the alpha 2 beta 2 heterotetrameric complex with essentially no alpha beta heterodimeric or free monomeric beta subunit species present. This suggests that the insulin receptor can reoxidize into the Mr 400,000 complex after the removal of DTT by gel filtration chromatography. Surprisingly, these apparently reoxidized insulin receptors were also observed to be functional with respect to insulin binding, albeit with a 50% decrease in affinity for insulin and insulin stimulation of the beta subunit autophosphorylation. To prevent reoxidation, the insulin receptors were pretreated with 50 mM DTT followed by incubation with excess N-ethylmaleimide prior to gel filtration chromatography in 0.1% Triton X-100. Under these conditions the insulin receptors migrated as the Mr 400,000 alpha 2 beta 2 complex.(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in heparan sulfate structure during transition from the proliferating to the non-dividing state of cultured arterial smooth muscle cells

Cultured arterial smooth muscle cells synthesize a cell-associated heparan sulfate proteoglycan which consists of a 92 kDa core protein with 3 to 4 heparan sulfate side chains covalently attached. Biosynthesis of the cell-associated heparan sulfate proteoglycan was compared in proliferating and in non-dividing vascular smooth muscle cells which are preincubated in the presence of [35]sulfate or a combination of [35S]methionine and [3H]glucosamine. The Mr of the core protein was identical in either growth state, but changes in the structure of the heparan sulfate side chains were observed. Non-dividing (postconfluent) arterial smooth muscle cells form longer heparan sulfate chains with a higher proportion of hydrophobic (N-acetyl) groups than proliferating (preconfluent) cells as judged from gel filtration experiments, hydrophobic interaction chromatography and heparitinase degradation. An enzyme preparation from proliferating cells catalyzes deacetylation and N-sulfation of heparan sulfate at a 5-fold higher activity than from non-dividing cells. Cell density-dependent structural differences of heparan sulfate are related to the finding that heparan sulfate isolated from non-dividing cells has a 10-fold higher antiproliferative potency than heparan sulfate from proliferating (preconfluent) cells.     

Structural features and some binding properties of proteoheparan sulfate enzymatically labeled by calf brain microsomes

Previous studies established that brain microsomes catalyze the transfer of [35S]sulfate from 3'-phosphoadenosine 5'-phospho[35S]sulfate to an O-linked oligosaccharide chain of a membrane glycoprotein and sulfamino groups of a membrane-associated proteoheparan sulfate (R. R. Miller and C. J. Waechter (1979) Arch. Biochem. Biophys. 198, 31-41). A large fraction of the proteoheparan [35S]sulfate can be released by treating the enzymatically labeled membranes from calf brain with 1 M NaCl. The salt-extracted 35S-labeled proteoglycan has been partially purified by a combination of ion-exchange and gel filtration chromatography. Based on chromatographic analyses, the 35S-labeled proteoglycan labeled in vitro is proposed to be a family of proteoheparan [35S]sulfates having an average molecular weight estimated to be 55,000. Variation in the length of the 35S-labeled polysaccharide chains partially accounts for the differences in molecular size of the proteoheparan [35S]sulfates. Binding studies reveal that the intact proteoheparan [35S]sulfates, as well as the free 35S-labeled polysaccharides released by mild alkali treatment, rapidly reassociate with calf brain membrane preparations. The association with calf brain membranes is saturable and reversible. Consistent with the binding being a specific interaction, only iduronic acid-containing glycosaminoglycans inhibit the association of the 35S-labeled proteoglycan with calf brain membranes and facilitate the disassociation. Neither the binding of the 35S-labeled proteoglycan to membranes nor the displacement was affected by hyaluronic acid, chondroitin 4-sulfate, or chondroitin 6-sulfate. The binding of the enzymatically labeled proteoheparan sulfate is reduced by preincubating membranes with either trypsin or chymotrypsin, but not with neuraminidase or phospholipase D. These results suggest that at least one class of proteoheparan sulfates could be specifically bound to one or more brain membrane proteins. The results also suggest a role for iduronosyl residues, and perhaps the stereochemical relationship of the carboxyl group to the O-sulfate moiety at C-2, in the recognition process.     

Characterization and solubilization of cyclo(His-Pro) binding from rat liver membranes

We have found cyclo(His-Pro) binding in rat liver plasma membranes. This study focused on the characterization of solubilized binding for cyclo(His-Pro) in rat liver membranes. The cyclo(His-Pro) binding of liver membranes was solubilized by digitonin and octyl-glucopyranoside. The efficiency of solubilization with digitonin was greater. However, cyclo(His-Pro) binding was not solubilized by Triton X-100, CHAPS, or Lubrol. Digitonin-solubilized membranes showed cyclo(His-Pro) binding with a high affinity constant (17 nM) and a low binding capacity (38 fmol/mg protein). Lectins from wheat germ, Bandeiraea simplicifolia II, Dolichos biflorus, Glycine max, and Tetragonolobus purpureas significantly adsorbed [3H]cyclo(His-Pro)-binding complex, but Bandeiraea simplicifolia I, Ricinus communis I, or Lens culinaris did not adsorb the binding complex. An analysis of [3H]cyclo(His-Pro)-associated membranes by high performance gel filtration chromatography showed a radioactive peak of Mr 200,000. These data indicate that cyclo(His-Pro) binding of rat liver membranes is solubilized by digitonin and is a glycoprotein of Mr 200,000.     

Analysis of the proteoglycans synthesized by human bone cells in vitro

Proteoglycans were isolated by ion-exchange chromatography from the extracted cell layer and culture medium of human bone cell cultures following incubation in the presence of [35S]sulfate and [3H]leucine. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), the synthesized proteoglycans consisted of at least five polydisperse species having median apparent Mr = 600,000, 400,000, 270,000, 135,000 and 40,000. When chromatographed further on octyl-Sepharose CL-4B, the proteoglycans of the cell layer resolved into three peaks. The unbound fraction (peak cell layer-I) contained a 40,000 species consisting of a single glycosaminoglycan chain with or without peptide. Peak cell layer-II contained three sulfated species on electrophoresis: a 600,000 species uniformly distributed across the peak, a 135,000 species enriched in the ascending limb (similar to bone PG-I as described previously), and a 270,000 species (similar to bone PG-I) enriched in the descending limb. Peak cell layer-III, eluting at 0.2% Triton X-100, was highly enriched in a 400,000 proteoglycan component. When media proteoglycans were chromatographed on octyl-Sepharose, two labeled peaks were found. Peak medium-I (unbound) contained a species exhibiting electrophoretic mobility similar to that of the 400,000 species present in peak cell layer-III. Peak II of the culture medium (medium-II) was apparently identical to that of peak cell layer-II, containing the 600,000, 270,000 and 135,000 species. No appreciable 40,000 species was observed in the medium. Treatment of the 600,000 species with either chondroitinase ABC or ACII generated a core protein preparation with bands of 390,000 and 340,000 on SDS gels. Neither the intact nor the chondroitinase ABC-treated 600,000 species was immunoprecipitated by a purified, polyclonal antiserum raised against the core protein of the large chondroitin sulfate proteoglycan of human articular cartilage. Treatment of the 270,000 and 135,000 proteoglycans with chondroitinase ABC, but not ACII, generated a core protein preparation with bands of 52,000 and 49,000 on SDS gels, indicating that they were dermatan sulfate-containing species. The 400,000 species contained both heparan sulfate and chondroitin sulfate, in approximately a 3:1 labeling ratio. This species changed in electrophoretic mobility following treatment with chondroitinase ABC, heparatinase, or both enzymes in combination, which suggested that it may be a hybrid proteoglycan (i.e. both types of glycosaminoglycan chain on the same core protein).(ABSTRACT TRUNCATED AT 400 WORDS)     

Isolation of in vivo radiolabeled proteoglycans from rat lung

Sulfated macromolecules of rat lung tissue were labeled in vivo with 35SO4 and extracted with a solution of 7 M urea containing 0.4% Triton X-100. DEAE-Sephacel chromatography separated sulfated macromolecules into three pools. Pool I consisted of high-molecular-weight, low-density sulfated glycoprotein, probably of mucous secretion origin. Pool II contained a mixture of proteoheparan sulfate and proteodermatan sulfate, together with core protein-free heparan sulfate chains. Pool III was very heterogeneous; its resolution into at least four proteoglycan species was achieved by CsCl density gradient centrifugation. Those included two (high- and low-density) species of proteoheparan sulfate, high-density proteochondroitin sulfate, and medium-density (1.45 less than rho less than 1.55 g/ml) proteodermatan sulfate.     

Purification and characterization of human placental microsomal aminopeptidase: immunological difference between placental microsomal aminopeptidase and pregnancy serum cystyl-aminopeptidase

Human placental microsomal aminopeptidase (microsomal PAP) was purified 3,880-fold from human placenta and characterized. The enzyme was solubilized from membrane fractions with Triton X-100 and also trypsin digestion, and subjected to zinc sulfate fractionation, chromatographies with DE-52, hydroxylapatite, Sephacryl S-300 and lentil lectin-Sepharose 4B, and finally affinity chromatography with bestatin-Sepharose 4B. Microsomal PAP was separated from aminopeptidase A (AAP) by affinity chromatography. The apparent relative molecular mass (Mr) of the enzyme was estimated to be 220,000 by high-performance liquid chromatography with an aqueous gel column. The purified enzyme gave almost a single band with a molecular mass of 140,000 by sodium dodecyl sulfate (SDS) gel electrophoresis. The isoelectric point of the enzyme was 5.2. The purified enzyme was most active at pH 8.0 with L-leucine-p-nitroanilide as substrate; the Km value for this substrate was 1.1 mmol/l. The microsomal PAP was immunologically different from the pregnancy serum cystyl aminopeptidase (serum PAP).     

Hydrodynamic properties of the gonadotropin receptor from a murine Leydig tumor cell line are altered by desensitization

The murine Leydig tumor cell line 1 (MLTC-1) contains gonadotropin receptors (GR) that are coupled to adenylate cyclase through the stimulatory guanine nucleotide binding protein (Gs). The binding of human choriogonadotropin (hCG) causes MLTC-1 cells to accumulate cAMP. With time, the ability of MLTC-1 cells to respond to hCG is attenuated by a process called desensitization. The hydrodynamic properties of GR from control and desensitized MLTC-1 cells were studied. Sucrose density gradient sedimentation in H2O and D2O and gel filtration chromatography were used to estimate the Stokes radius (a), partial specific volume (vc), sedimentation coefficient (S20,w), and molecular weight (Mr) of the detergent-solubilized hormone-receptor complex (hCG-GR). [125I]hCG was bound to MLTC-1 cells under conditions that allow (37 degrees C) or prevent (0 degree C) desensitization, and hCG-GR was solubilized in Triton X-100. In the absence of desensitization, control hCG-GR had a Mr of 213,000 (a = 6.2; vc = 0.76; S20,w = 7.3), whereas desensitized hCG-GR had a Mr of 158,000 (a = 6.1; Vc = 0.71; S20,w = 6.6). Deglycosylated hCG (DG-hCG) is an antagonist that binds to GR with high affinity but fails to stimulate adenylate cyclase or cause desensitization. [125I]DG-hCG was bound to MLTC-1 cells and DG-hCG-GR solubilized in Triton X-100. The hydrodynamic properties of DG-hCG-GR (Mr 213,000; a = 5.8; Vc = 0.77; S20;w = 7.6) were the same as that for control hCG-GR. There was no evidence for the association of adenylate cyclase or Gs with GR in Triton X-100 solubilized preparations.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characterization of rat and human steroid sulfatases

Rat and human steroid sulfatases were purified from liver and placenta, respectively, by the same procedure. The rat and human enzymes were solubilized with Triton X-100, and purified by immunoaffinity chromatography with a monoclonal antibody showing high binding activities to both the enzymes. They were further purified by high-pressure anion-exchange chromatography to compare their structural and catalytic properties. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that both enzymes had a molecular weight of 62,000. The enzymes had similar amino acid compositions and amino-terminal amino acid sequences. Significant differences of the optimum pH, Michaelis constant and maximum velocity were observed between these enzymes. The optimum pH of each enzyme varied from 6.0 to 8.0, depending on substrates and with or without Triton X-100. In detergent-free media, steroid sulfates competitively inhibited the ability of these enzymes to hydrolyze 4-nitrophenyl sulfate. In media containing Triton X-100, on the other hand, the inhibition types of the steroid sulfates on the hydrolyzing activities of the rat and human enzymes were noncompetitive- and mixed-types, respectively.     

Covalent labelling of the lutropin binding site. Evidence for a single Mr 90000 sialoglycopolypeptide.

Membrane-associated sialoglycopolypeptides of rat ovaries were oxidized with NaIO4, reduced with NaB3H4 and solubilized with Triton X-100. The solubilized proteins carrying the 3H label were subjected to affinity chromatography on human choriogonadotropin coupled to agarose. Polyacrylamide-gel electrophoresis in sodium dodecyl sulphate followed by fluorography revealed a single component of apparent Mr 90000. This component was abolished when ovaries saturated with choriogonadotropin were used as starting material. The above result is identical to that obtained previously by conventional detection methods [ Metsikk ö & Rajaniemi (1982) Biochem. J. 208, 309-316] and indicates that the 3H-labelled lutropin/choriogonadotropin sialoglycopolypeptide was observed. The affinity-purified 3H-labelled protein co-eluted with the choriogonadotropin-binding activity solubilized with Triton X-100 from rat ovarian particles, showed a Stokes' radius of 6.2 nm and sedimented as a single band with a sedimentation coefficient of 5.1 S. The sedimentation coefficient of this 3H-labelled protein was not significantly altered when boiled in 1% sodium dodecyl sulphate, indicating that non-covalently associated subunits were not present. The 3H-labelled protein cosedimented with the choriogonadotropin-binding activity solubilized with Triton X-100 from rat ovary. When 125I-choriogonadotropin-receptor complex was covalently crosslinked with glutaraldehyde, an Mr 130000 component was produced as detected by sodium dodecyl sulphate gel electrophoresis. This component was extracted from the polyacrylamide gel and subjected to sucrose-density-gradient centrifugation in 0.1% Triton X-100. A single band sedimenting at the position of the 125I-choriogonadotropin-receptor complex solubilized from a prelabelled ovary was observed, exhibiting a sedimentation coefficient of 6.5S. These data suggest that the lutropin-binding site is a single sialoglycopolypeptide of Mr 90000, which binds one molecule of hormone resulting in an apparent Mr 130000 complex. The large Stokes' radius (6.2 nm) of the binding site is accounted for by bound detergent.     

Characterization of the receptor for platelet-derived growth factor on human fibroblasts. Demonstration of an intimate relationship with a 185,000-Dalton substrate for the platelet-derived growth factor-stimulated kinase

The receptor for platelet-derived growth factor (PDGF) on human foreskin fibroblasts has been characterized. The molecular weight of the PDGF-receptor complex was estimated by affinity labeling techniques to about 200,000, as determined by sodium dodecyl sulfate-gel electrophoresis performed under reducing conditions. Subtraction of the Mr of reduced PDGF (18,000 to 15,000) gives a Mr for the receptor proper of 185,000 (+/- 10,000). The mobility in sodium dodecyl sulfate-gel electrophoresis was similar whether or not reducing agents were present, suggesting that the receptor may be a single chain protein. The hydrodynamic size of the 125I-PDGF-receptor complex after solubilization with Triton X-100, corresponded to a Mr of approximately 320,000, as determined by gel chromatography. Subtraction of the Mr contributions from Triton X-100 and PDGF, respectively, gives a Mr of approximately 200,000 for the receptor itself, an estimate in good agreement with the value obtained from the affinity-labeling experiments. Several lectins were analyzed for their ability to inhibit binding of 125I-PDGF to its receptor. It was found that wheat germ agglutinin and a lectin from Crotalaria juncea were effective inhibitors and that their inhibitory effects could be neutralized by N-acetylglucosamine and galactose, respectively, suggesting that the receptor contains these sugars. The properties of the receptor were compared with those of a 185,000-Da component, being the major substrate for the membrane-bound PDGF-stimulated kinase. It was found that the 185,000-Da component behaved similar to the PDGF receptor in sodium dodecyl sulfate-gel electrophoresis, performed with or without reducing agents present. Further, the 185,000-Da component co-eluted with the PDGF receptor on a Sepharose 6B column, and had affinity for the same lectins that inhibited the binding of 125I-PDGF to its receptor. Finally, the 185,000-Da component had affinity for PDGF immobilized on Sepharose beads, suggesting that it has PDGF-binding activity. We conclude that the PDGF receptor and the 185,000-Da substrate for the PDGF-dependent kinase are intimately related and probably identical molecules.     

Analysis of the proteoglycans synthesized by corneal explants from embryonic chicken. II. Structural characterization of the keratan sulfate and dermatan sulfate proteoglycans from corneal stroma

Radioisotopically labeled proteoglycans were isolated from a 4 M guanidine HCl, 2% Triton X-100 extract of corneal stroma from day 18 chicken embryos by anion-exchange chromatography. Two predominant proteoglycans in the sample were separated by octyl-Sepharose chromatography using a gradient elution of detergent in 4 M guanidine HCl. One proteoglycan had an overall mass of approximately 125 kDa, a single dermatan sulfate chain (approximately 85-90% chondroitin 4-sulfate, low iduronate content) of approximately 65 kDa, and a core protein after chondroitinase ABC digestion of approximately 45 kDa which also contained one to three N-linked oligosaccharides and one O-linked oligosaccharide. The other proteoglycan had an overall size of approximately 100 kDa, two to three keratan sulfate chains of approximately 15 kDa each, and a core protein following keratanase digestion of approximately 51 kDa which included two to three N-linked but no O-linked oligosaccharides. A larger size, a greater overall hydrophobicity (as measured by its interaction with octyl-Sepharose) and an absence of O-linked oligosaccharides argue that this core protein is a distinct gene product from the core protein of the dermatan sulfate proteoglycan.     

Purification, properties and partial amino acid sequence of the blood-group-A-gene-associated alpha-3-N-acetylgalactosaminyltransferase from human gut mucosal tissue.

An alpha-3-N-acetylgalactosaminyltransferase that transfers N-acetylgalactosamine from UDP-N-acetylgalactosamine to H-active structures to form A determinants was purified to homogeneity from human gut mucosal tissue of blood-group-A subjects. The mucosa was homogenized, then treated with Triton X-100, and the solubilized enzyme was purified by affinity chromatography on UDP-hexanolamine-agarose and octyl-Sepharose CL-4B. Enzyme activity was recovered in 44% yield with a specific activity of approx. 7 mumol/min per mg. The only effective acceptor substrates for the transferase were those containing a subterminal beta-galactosyl residue substituted at the O-2 position with L-fucose. The purified enzyme had a weak capacity to transfer D-galactose from UDP-D-galactose to similar acceptors to make blood-group-B determinants. H.p.l.c. and SDS/PAGE analysis indicated an Mr of 40,000 for the purified enzyme. For the first time a partial amino acid sequence Xaa-Ser-Leu-Pro-Arg-Met-Val-Tyr-Pro-Gln-Ile-Ser?-Val-Leu was obtained for the N-terminal region of the soluble alpha-3-N-acetylgalactosaminyltransferase.     

Purification of the type II insulin-like growth factor receptor from rat placenta

The membrane receptor for insulin-like growth factor II (IGF II) has been purified to near homogeneity from rat placenta by chromatography of crude plasma membranes solubilized in Triton X-100 on agarose-immobilized IGF II. Elution of the IGF II receptor from the matrix at pH 5.0 in the presence of 1.5 M NaCl resulted in a receptor purification of 1100-fold from isolated plasma membranes, or 340-fold from the Triton extract with an average yield of about 50% in five separate purifications. Analysis of 125I-IGF II binding to the solubilized receptor in the Triton extract and in purified form by the method of Scatchard demonstrated no change in receptor affinity (Kd = 0.72 nM). Sodium dodecyl sulfate electrophoresis of the purified receptor showed one major band at Mr = 250,000 with only minor contamination. Affinity labeling of the receptor in isolated placenta membranes and in purified form using 125I-IGF II and the cross-linking agent disuccinimidyl suberate resulted in covalent labeling of only the Mr = 250,000 band. Such labeling was abolished by unlabeled IGF II but was unaffected by insulin, consistent with the previously reported specificity of IGF II receptor (Massague, J., and Czech, M.P. (1982) J. Biol. Chem. 257, 5038-5045). These results establish a one step affinity method for the purification of the type II IGF receptor that is rapid and highly efficient.