Components of the major urinary protein complex of inbred mice: Separation and peptide mapping

Gel filtration of the nondialyzable fraction of urine from normal inbred mice on Sephadex G-100 yielded three peaks (I, II, and III in order of elution), the relative sizes of which varied with the sex and strain of the mice. Constituents of peak I, the breakthrough peak, included uromucoid (Tamm-Horsfall mucoprotein); peak III was low in nitrogen, rich in carbohydrate, nonprecipitable with trichloroacetic acid, gave no definitive ultraviolet or visible spectrum, and had a sedimentation coefficient of 0.5 S. Peak II contained the electrophoretically distinguishable prealbumins of the major urinary protein (MUP) complex. These components (known as 1, 2, and 3 in order of increasing mobility toward the anode) were separated by chromatography on diethylaminoethyl cellulose. Tryptic peptide mapping indicated that components 1 and 2, a genetic variant shown to be under the control of one genetic locus (the Mup-alocus), differed by a single peptide. Components 1 and 3 had a number of peptides in common plus several peptides unique to each. The peptide map of any given component did not differ between sexes or between the strains investigated.     

Histochemistry of mucosubstances in Brunner's-gland cells and duodenal goblet cells of two New World monkey species (Saimiri sciureus andSaguinus fuscicollis)

Summary Duodenal goblet cells and Brunner's-gland cells obtained from two species of New World monkeys (Saimiri sciureus andSaguinus fuscicollis) were studied using conventional histochemical methods and by applying a panel of 17 labelled lectins. The secretions of both goblet and Brunner'-gland cells were found to contain neutral mucosubstances, while those of goblet cells also exhibit acid and sulphated carbohydrate components. Lectin binding studies allowed a more detailed analysis of the mucus glycoproteins. Marked differences between the two examined species were not detected.N-Acetyl-galactosamine, galactose, fucose andN-Acetyl-glucosamine were found to be the predominante sugar residues in Brunner's-glands glycoproteins, with mannose and glucose being only minor components.Dedicated to Professor Dr. T.H. Schiebler on the occasion of his 65th birthday     

Behaviors on gel-filtration and electrophoresis of 6-phosphogluconate dehydrogenase isozymes isolated from sweet potato

Sephadex G-200 gel-filtration of an enzymatic preparation fromsweet potato root tissue showed three activity peaks (I, IIand III) of 6-phosphogluconate dehydrogenase. Re-chromatographyof either Peak II or III produced two peaks corresponding toPeak II and III. Disc electrophoreses of the original preparation,Peak II, Peak III and the Peak II-like peak after re-chromatographygave idetical zymograms of the three isozymes which were notinterconvertible. ¹ Present address: Institute of Applied Microbiology, Universityof Tokyo, Bunkyo-ku, Tokyo 113, Japan. (Received May 30, 1972; )     

Occurrence of Nuclease P1-Malonogalactan Complex

Nuclease P₁ from Penicillium citrinum was found to be produced in a form of complex with malonogalactan (a galactan, 1, 5-β-galactofuranoside polymer esterfied with malonic acid at position 3) in the culture on wheat bran. Neither nuclease P₁-malonogalactan complex nor malonogalactan was produced in a liquid medium. Nuclease P₁-malonogalactan complexes, P₁-MG I, II, and III were purified from an aqueous extract of the culture on wheat bran. The most anionic complex, P₁-MG III, was composed of the protein, carbohydrate and malonic acid in the ratio of 1: 2.6: 0.5 (w/w). The complex was not dissociated by purification procedures including fractionations with acetone and ammonium sulfate, gel filtration and DEAE-cellulose chromatography. A malonogalactan-specific carboxylesterase was found in culture of the same mold on wheat bran. Nuclease P₁-malonogalactan was demalonylated by the esterase to yield nuclease P₁-galactan. The binding of nuclease P₁ to galactan was rather loose so that nuclease P₁-galactan complex was partially dissociated by DEAE-cellulose chromatography. Attempt to reconstitute the complex from nuclease P₁ and malonogalactan upon mixing was unsuccessful. Exogenously supplemented nuclease P₁ did not associate with malonogalactan in the growing culture on wheat bran, either.

Several extracellular enzymes such as RNase, β-galactosidase and protease were also found in a form of complex with malonogalactan in the culture on wheat bran.     

Biochemical Characterization of Two Distinct Angiotensin AT2 Receptor Populations in Murine Neuroblastoma N1E-115 Cells

Abstract: The murine neuroblastoma N1E-115 cell line possesses a high density of angiotensin II (Angll) receptors that can be solubilized with the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate. These solubilized binding sites exhibited high affinity for CGP-42112A and not Losartan, indicating that they were of the AT₂ subtype. However, displacement of ¹²⁵I-Angll with the AT₂ nonpeptide antagonist PD-123319 resulted in a biphasic curve, suggesting heterogeneity of the AT₂ receptor population in N1E-115 cells. In support of this view, separation of two receptor populations was accomplished with heparin-Sepharose chromatography. More specifically, three distinct protein peaks eluted from the heparin-Sepharose column, two of which bound ¹²⁵I-Angll with high affinity and saturability. One of these binding peaks (peak I) eluted rapidly and represented ～80% of the total binding activity, whereas the remaining binding activity was contained within a second peak (peak III) that required the addition of 1.5 M NaCI for its complete elution. Pharmacological analysis revealed that both peaks of binding activity were exclusively AT₂ receptors insofar as they exhibited high affinity for CGP-42112A and little or no affinity for the AT₁-selective antagonist Losartan. However, whereas the nonpeptidic AT₂-selective antagonist PD-123319 completely displaced the binding of ¹²⁶I-Angll from peak I in a monophasic fashion (IC₅₀= 9.1 ± 4.1 nM; mean ± SEM; n = 3), PD-123319 was much less effective in displacing ¹²⁵I-Angll from peak III (IC₅₀= 196 β 27 nM; mean β SEM; n = 3). Treatment of individual peaks with the reducing agent dithiothreitol caused a large increase in ¹²⁵I-Angll specific binding in peak III, whereas a decrease in binding was observed in peak I. Moreover, GTPγS significantly reduced high-affinity agonist binding in peak I but not peak III, further suggesting heterogeneity in the AT₂ receptor family. Finally, immunoblotting studies with polyclonal antisera raised against peak I specifically detected two proteins of 110 and 66 kDa, as is true in crude solubilized membranes, whereas no immunospecific proteins were detected in peak III. These same antisera immunoprecipitated ¹²⁵I-Angll binding activity in peak I but were ineffective in peak III. Collectively, these results suggest that heparin-Sepharose chromatography can efficiently separate two pharmacologically, biochemically and immunologically distinct populations of AT₂ receptors.     

Carbohydrates of Influenza Virus. I. Glycopeptides Derived from Viral Glycoproteins After Labeling with Radioactive Sugars

The carbohydrate moiety of the influenza glycoproteins NA, HA₁, and HA₂ were analyzed by labeling with radioactive sugars. Analysis of glycopeptides obtained after digestion with Pronase indicated that there are at least two different types of carbohydrate side chains. The side chain of type I is composed of glucosamine, mannose, galactose, and fucose. It is found on NA, HA₁, and HA₂. The side chain of type II contains a high amount of mannose and is found only on NA and HA₂. The molecular weights of the corresponding glycopeptides obtained from virus grown in chicken embryo cells are 2,600 for type I and 2,000 for type II. The glycoproteins of virus grown in MDBK cells have a higher molecular weight than those of virus grown in chicken embryo cells, and there is a corresponding difference in the molecular weights of the glycopeptides. Under conditions of partial inhibition of glycosylation, virus particles were isolated that contained hemagglutinin with reduced carbohydrate content. Glycopeptide analysis indicated that this reduction is due to the lack of whole carbohydrate side chains and not to the incorporation of incomplete ones. This observation suggests that glycosylation of the viral glycoproteins involves en bloc transfer of the core sugars to the polypeptide chains.     

Hormonal effects on fat cell adenosine 3′,5′-monophosphate dependent protein kinase

Fat cell extracts were electrophoresed on polyacrylamide gels to separate the regulatory subunit and holoenzyme species of protein kinase. Gels were incubated with cyclic [³H]AMP ([³H]cAMP) and washed, and the bound [³H]cAMP was estimated. The band of [³H]cAMP found closest to the origin (Peak I) was associated with cAMP-dependent protamine kinase activity. A seond [³H]cAMP peak (Peak II) also contained protamine kinase activity. Although the kinase activity of Peak II was much less than Peak I, more [³H]-cAMP was bound in Peak II than in Peak I. The [³H]cAMP peak furthest from the origin (Peak III) was devoid of kinase activity.Incubation of extracts with cAMP prior to electrophoresis diminished or abolished kinase activity in Peaks I and II. This incubation also decreased [³H]cAMP binding in Peaks I and II, and increased binding in Peak III. When extracts were incubated with [³H]cAMP before electrophoresis, essentially all of the radioactivity was found in Peak III. It was concluded that Peak I represents a holoenzyme form and that Peak III is composed of the regulatory subunits of this enzyme. Peak II may represent a relatively inactive holoenzyme form not previously described.Incubation of adipocytes with epinephrine resulted in a dose- and time-dependent decrease in Peak I and increase in Peak III, and insulin opposed these effects of epinephrine. After 1-min incubations with epinephrine, the decreases in Peak I or increases in Peak III correlated with increases in phosphorylase a activity, decreases in glycogen synthase I activity and changes in cAMP, both in the presence and absence of insulin. However, after incubation with epinephrine for more than 2 min in the presence of insulin, phosphorylase a activity did not correlate with cAMP, suggesting that factors other than the cyclic nucleotide mediate the effects of epinephrine and insulin.     

DNA-dependent RNA polymerases from murine testis. Properties of two activities.

Multiple forms of DNA-dependent RNA polymerase activities have been isolated from nuclei of mouse testis. Using highly purified nuclei, two activities can be solubilized and are separable by DEAE-Sephadex chromatography; peak I eluting at 0.11–0.14 M and peak II eluting at 0.24–0.27 M (NH₄)₂SO₄. A third form of RNA polymerase activity is observed eluting at 0.31–0.33 M (NH₄)₂SO₄ when an extract from a less highly purified nuclear preparation is analysed. At concentrations of 0.125 μg/ml, peak I is insensitive to the toxin α-amanitin, peak II is totally inhibited, and peak III is partially inhibited. Peak I activity is optimal at pH 8.4 in the presence of Mg²⁺ (2–6 mM) or Mn²⁺ (1 mM) and uses native and heat-denatured DNA template equally well. Peak II has optimal activity at pH 7.9 in the presence of Mn²⁺ (2 mM) and heat-denatured DNA. Mg²⁺ has little effect on the activity of peak II.     

Studies on the biochemistry and fine structure of silica-shell formation in diatoms

Summary The distribution of radioactivity in ethanol-water-soluble compounds after short periods of photosynthetic incorporation of ¹⁴CO₂ is consistent with the operation of the photosynthetic carbon reduction (PCR) cycle in the fresh water diatom Navicula pelliculosa. Incorporation of ¹⁴CO₂ for extended time periods established the presence of the intermediates of the PCR and tricarboxylic acid (TCA) cycles, amino acids, and organic acids; free sugars were not observed. The main labelled soluble carbohydrate was a glucan. Hydrolysis of the radioactive insoluble material indicated the presence of carbohydrates containing several distinct sugars, and proteins with the usual amino-acid composition. During silicon starvation of exponentially growing cultures, rates of incorporation of both ³²P _i and ¹⁴CO₂ decreased. Incorporation into the lipid increased, with a corresponding decrease into protein and carbohydrate. Reintroduction of Si to staryed cells led to an increased rate of incorporation of both isotopes, and transient changes in the radioactivity in most metabolic intermediates investigated. After 30 min the radioactivity in all PCR cycle intermediates, except phosphoglyceric acid, had increased by about 300%. The radioactivity of citrate and -keto-glutarate increased, whereas that of other TCA-cycle intermediates decreased. An initial decrease in the levels of glutamate, aspartate and glutamine was apparently reversed by cleavage of glutamate-aspartate peptides, as radioactivity of other amino acids increased. Incorporation into the soluble glucan and into protein increased markedly although the rate of incorporation into insoluble carbohydrates remained constant.     

Disposition of fucose in brain

Abstract— Labelled fucose administered to rats in vivo was rapidly incorporated into brain glycoproteins, but not into any other brain constituents, including glycolipids and acid mucopolysaccharides. Maximum incorporation of tritium-labelled fucose into brain glyco-proteins occurred 3–6 h after intraperitoneal injection in young or adult rats, and the half-time for the turnover of glycoprotein-fucose in young rats was approximately 2 weeks. Within 3 h after the administration of either [1-³H]fucose or fucose generally labelled with tritium, 75 per cent of the total acid-soluble radioactivity in plasma and brain was found to be volatile, and by 24 h after injection more than 90 per cent of the acid-soluble radioactivity was volatile. The tritium in labelled fiicose appears to undergo arapid exchange reaction with hydrogen atoms in body water, although the tritium in fucose glycosidically- linked to glycoproteins is biologically stable. The rapid disappearance of labelled free fucose from the plasma and tissues of the rat precludes the possibility of any significant degree of reutilization of labelled precursor, and provides support for other data indicating that the turnover of fucose in brain glycoproteins is relatively slow in comparison to that of hexosamine and sialic acid. Activities of α-L-fucosidase in rat brain, with pH optima at 40 and 6.0, had essentially the same K_m (4 × 10^?4 M and 3.2 × 10^?4 M, respectively) with p-nitrophenyl-α-L-fucopyranoside as substrate. Activities of both were competitively inhibited by L-fucose. However, the K_t measured at pH 4 (1.9 × 10^?2) was almost ten times greater than that measured at pH 6 (1.5 × 10^?4).     

Purification, properties, and partial structure elucidation of a high-molecular-weight glycoprotein from cervical mucus of the bonnet monkey (Macaca radiata).

A high-molecular-weight glycoprotein has been purified from the cervical mucus of the bonnet monkey (Macaca radiata). The glycoprotein was shown to be homogeneous by electrophoresis, sedimentation equilibrium, and N-terminal group determination, and to contain 19% protein, 19% D-galactose, 18% N-acetyl-D-galactosamine, 15% N-acetyl-D-glucosamine, 11% L-fucose, 10% sialic acid, and 1% sulfate groups, corresponding to about 1800 amino acid residues and 400 carbohydrate side chains of about 9 monosaccharides. The carbohydrate chains are linked to the peptide backbone through N-acetyl-D-galactosamine and serine (or threonine) residues. Reduction with dithiothreitol and alkylation with iodoacetic acid reduced the molecular mass from 1 to 0.5 X 10(6) daltons and produced subunits having the same size, charge, and N-terminal amino acid. Electrophoretic studies suggested the presence of disulfide bonds between two chains of the glycoprotein. Degradation with alkaline borohydride gave, after fractionation on Bio-Gel P-2, fractions containing L-fucose, D-galactose, N-acetyl-D-galactosaminitol, N-acetyl-D-galactosamine, N-acetyl-D-glucosamine, and sialic acid in the ratio of 1.0:3.0:1.0:1.0:1.3:1.0. Further fractionation by electrophoresis and paper chromatography gave a charged fraction representing 13% of the original glycoprotein. Enzymic degradation and methylation studies indicated the presence of the structure alpha-Gal-(1 leads to 3)-[Fuc(1 leads to 2)]-Gal-(1 leads to 4)-GlcNAc, linked to a core component containing N-acetyl-D-galactosaminitol.     

Partial purification and kinetic properties of three different d-glucosamine 6-P:N-acetyltransferase forms from human placenta

Three distinct forms of -glucosamine 6-P (Gm 6-P):N-acetyltransferases (EC 2.3.1.4) were partially purified from human placental homogenates by carboxy methyl-Sephadex chromatography. Purification of forms I and II were 13.5-fold, while that of form III was 114-fold. All three forms had a pH optimum value of 9.7 in glycine–NaOH buffer. Enzymes II and III had a K_m value for Gm 6-P of 3.0 mM, which was less than half of that observed for form I (7.1 mM). The corresponding K_m values for acetyl CoA were 0.157 (form I), 0.187 (form II) and 0.280 mM (form III), respectively. Activities of all three forms were inhibited at high concentrations of either substrate. These enzymes were inhibited from 82 to 92% by 2.5 mM p-chloromercuribenzoate. The inhibition was largely reversible by inclusion of 2.5 mM dithiothreitol in the incubation mixtures. There was no requirement for divalent cations, as demonstrated by lack of inhibition of enzyme activity by ethylene diamine tetraacetate. The results are discussed in terms of differences among the enzyme properties of human placental, rodent and porcine liver forms.     

Carbohydrate composition and electrophoretic properties of tomato polygalacturonase isoenzymes

Two polygalacturonase isoenzymes, PG I and PG II, were extracted from Murrieta tomato and purified by gel exclusion and ion-exchange chromatography. The kinetic constants and activation energies of the purified isoenzymes have been determined. Polygalacturonase I has two polypeptide chains (Mr = 47 500 and 41 400) whereas polygalacturonase II is a single polypeptide (Mr = 47 500) as shown by electrophoresis in polyacrylamide gels in the presence of sodium dodecyl sulphate. Both isoenzymes are glycoproteins. Through gas liquid chromatography, polygalacturonase II was shown to contain 4.6% neutral hexoses and 1.5% amino sugars. There are eight D-mannose, two L-fucose, two D-xylose and three N-acetylglucosamine residues per mole of PG II. The carbohydrate portion of PG II was shown to be attached to the protein part through an N-acetylglucosaminylasparaginyl bond.     

The isolation and partial characterization of a glycoprotein isolated from human gastric aspirates and from extracts of gastric mucosae

The isolation and partial characterization of a glycoprotein isolated from individual gastric aspirates and extracts of gastric mucosae solubilized with N-acetylcysteine is described.The isolated glycoproteins and the glycoproteins from proteolysed gastric aspirates showed virtually the same carbohydrate and amino acid composition. The results indicate that they consist of a protein core to which are attached carbohydrate side-chains composed of four sugars: N-acetylgalactosamine N-acetylglucosamine, galactose, fucose showing a ratio of 1 : 3 : 4 : 2. Superimposed on this basic structure were additional sugar residues, the blood-group determinants. The results also suggest that the carbohydrate side-chains are linked by an alkali-labile O-glycosidic linkage to the threonine and serine residues of the protein core, N-acetylgalactosamine forming the link.     

Effect of chloroquine on the degradation of L-fucose and the polypeptide moiety of plasma membrane glycoproteins

To evaluate the role of lysosomes in the breakdown of the carbohydrate and the polypeptide moiety of plasma membrane glycoproteins, degradation of the plasma membrane glycoprotein gp120 was studied in the liver of rats treated with the lysosomotropic amine chloroquine. Half-lives of degradation of the terminal sugar L-fucose and of L-methionine of gp120 were measured in isolated plasma membranes after pulse-chase experiments in vivo. Chloroquine extended the plasma membrane half-life of the polypeptide moiety of gp120 from 51 h to 143 h. By contrast, L-fucose of gp120 in the plasma membrane was not affected by chloroquine, but decayed with the same short half-lives of 22 h and 23 h in both controls and chloroquine-treated rats. The data suggest that the protein portion of gp120 is degraded within the lysosomes. Conversely, the terminal sugar L-fucose is removed from the glycoprotein independent from proteolysis before segregation of the glycoprotein into the lysosomal compartment.     

Effects of prostaglandin E1 on the metabolism in rat parathyroid gland in vitro

We investigated some effects of prostaglandin E₁ on the metabolism of rat parathyroid glands using a culture system containing basal Eagle's medium supplemented with 5–10% heat-inactivated rat serum. Rat parathyroid glands incorporate [³H]fucose and ¹⁴C-labeled amino acids into cellular glycoproteins and secrete some of these into the culture medium. Gel filtration chromatography separates these glycoproteins into three classes, the smallest of which (peak 3) is secreted with immunoreactive parathyroid hormone. In cultures of 48 h, prostaglandin E₁ (1 μg/ml) specifically inhibits the secretion of peak 3 and of parathyroid hormone but has no effect on the incorporation of [³H]-fucose, ¹⁴C-labeled amino acids, or [³H]uridine into parathyroid glands. Cytochalasin B inhibits the secretion of parathyroid hormone and the incroporation of isotopic fucose and amino acids. Cortisol stimulates incorporation of [³H]fucose and the secretion of parathyroid hormone even in the presence of inhibitory doses of prostaglandin E₁. It is concluded that, in organ culture, prostaglandin E₁ inhibits the secretion of parathyroid hormone and of a specific glycoprotein the function of which may be related to the secretion of the hormone.     

Glycosylation characteristics of pigmentation-associated antigen (GP75): an intracellular glycoprotein of human melanocytes and malignant melanomas

Pigmentation-associated antigen (PAA) or gp75 is a glycoprotein localized to the melanosomes of human melanomas and melanocytes to which a mouse monoclonal antibody (AbTA99) has been produced (T. M. Thomson et al. (1985) J. Invest. Dermatol. 85, 169). Treatment of 3H-labeled immunoprecipitated melanoma PAA with alkaline-borohydride, hydrazinolysis, or N-glycanase released three families of carbohydrate chains (I, II, and III). Peak I consists of a major component (Ia) of sialylated triantennary N-linked chains which are partially substituted with fucose on terminal positions as well as on the chitobiose core and a minor component (Ib) which is a sialylated biantennary N-linked species. Peak II was not well characterized but may be a monoantennary complex chain species. Peak III consists of typical N-linked high mannose units with six to seven mannose residues. Melanocyte PAA carbohydrate chains have the same general features as melanoma PAA except that the biantennary complex chain predominates; this difference resembles that observed between the cell surface glycopeptides of transformed animal cells and their nontransformed counterparts. The glycosylation characteristics of this melanosomal glycoprotein are compared with those of glycoproteins from endoplasmic reticulum, Golgi, and lysosomes, and with tyrosinase. It is suggested that the glycosylation pattern is a reflection of the biosynthetic origin and cellular destination of a particular organelle and its constituents.     

The effect of castanospermine on the synthesis of synaptic glycoproteins by rat brain slices

Slices were prepared from rat forebrains and the incorporation of [³H]mannose and [³⁵S]methionine into proteins and glycoproteins determined. The incorporation of methionine continued to increase for up to 8 hours whereas mannose incorporation was maximal between 2 and 4 hours and declined thereafter. Glycopeptides prepared by pronase digestion of [³H]mannose-labeled glycoproteins were digested with endoglucosaminidase H (endo H) and analysed by gel filtration. The major endo H-sensitive oligosaccharide eluted in a position similar to standard Man₈GlcNAc. In the presence of castanospermine, which inhibits glucosidase I, the first enzymatic step in the processing of N-linked oligosaccharides, a new endo H-sensitive glycan similar in size to standard Glc₃Man₉GlcNAc₂ accumulated. Synaptic membranes (SMs) were isolated from slices which had been incubated with either [³H]mannose or [³⁵S]methionine in the presence and absence of castanospermine. In the presence of inhibitor the relative incorporation of [³H]mannose into high-mannose glycans of synaptic glycoproteins was increased. The incorporation of newly synthesized, [³⁵S] methioninelabeled, Con A-binding glycoproteins into SMs was not affected by the addition of inhibitor. Many of the glycoproteins synthesized in the presence of castanospermine exhibited a decreased electrophoretic mobility indicative of the presence of altered oligosaccharide chains. The results indicate that changes in oligosaccharide composition produced by castanospermine had little effect on the subsequent transport and incorporation of glycoproteins into synaptic membranes.To whom to address reprint requests.     

Glycoconjugate histochemistry of the digestive tract of <Emphasis Type="Italic">Triturus carnifex</Emphasis> (Amphibia,Caudata)

Summary In this study, the variety of sugar residues in the gut glycoconjugates of Triturus carnifex (Amphibia, Caudata) are investigated by carbohydrate conventional histochemistry and lectin histochemistry. The oesophageal surface mucous cells contained acidic glycoconjugates, with residues of GalNAc, Gal β1,3 GalNAc and (GlcNAc β1,4) _n oligomers. The gastric surface cells mainly produced neutral glycoproteins with residues of fucose, Gal β1-3 GalNAc, Gal-αGal, and (GlcNAc β1,4) _n oligomers in N- and O-linked glycans, as the glandular mucous neck cells, with residues of mannose/glucose, GalNAc, Gal β1,3 GalNAc, (GlcNAc β1,4) _n oligomers and fucose linked α1,6 or terminal α1,3 or α1,4 in O-linked glycans. The oxynticopeptic tubulo-vesicular system contained neutral glycoproteins with N- and O-linked glycans with residues of Gal-αGal, Gal β1-3 GalNAc and (GlcNAc β1,4) _n oligomers; Fuc linked α1,2 to Gal, α1,3 to GlcNAc in (poly)lactosamine chains and α1,6 to GlcNAc in N-linked glycans. Most of these glycoproteins probably corresponds to the H⁺K⁺-ATPase β-subunit. The intestinal goblet cells contained acidic glycoconjugates, with residues of GalNAc, mannose/ glucose, (GlcNAc β1,4) _n oligomers and fucose linked α1,2 to Gal in O-linked oligosaccharides. The different composition of the mucus in the digestive tracts may be correlated with its different functions. In fact the presence of abundant sulphation of glycoconjugates, mainly in the oesophagus and intestine, probably confers resistance to bacterial enzymatic degradation of the mucus barrier.     

Synthesis and migration of proteins and glycoproteins in juxtaglomerular cells of sodium-deficient rats

Summary Sections of juxtaglomerular cells from sodium-deficient rats were subjected to radioautography after a single intravenous injection of L-tyrosine3,5 ³H or of L-fucose ³H to identify the sites of synthesis and to follow the migration of newly-formed proteins and glycoproteins. As early as 2 min after injection of L-tyrosine ³H, the label was highest in the rough endoplasmic reticulum (RER), suggesting that cisternal ribosomes are sites of protein synthesis. By 60 min, much of the label had migrated from the RER to the Golgi complex. Some radioactivity was already present over specific granules by 2 min but a peak was reached at 4h. The label over myofilaments was evident at all time intervals, indicating a certain incorporation of tyrosine into their contractile and/or structural proteins. The label over the cell surface peaked at 4h. After injection of L-fucose ³H, there was an early and important relative specific radioactivity in the Golgi complex at 5 min with a peak at 20 min and a decrease thereafter. The label increased slightly but steadily in secretory granules and cell surface to reach maxima at 4 h. A low level of radioactivity was recorded in mitochondria at all time intervals. After injection of both fucose ³H and tyrosine ³H, the label was detected at relatively low levels in the cytosol. These results suggest that renin, as the major secretory glycoprotein of juxtaglomerular cells, is synthetized in the RER, packaged in the Golgi complex and found relatively rapidly in newly-formed secretory granules. Part of the fucose and tyrosine labels is also associated with the thick cell coat of these cells.Recipient of a summer fellowship from the Kidney Foundation of Canada