Carbohydrate Composition of Variant-Specific Surface Antigen Glycoproteins from Trypanosoma brucei

SYNOPSIS. The carbohydrate of variant-specific surface antigen glycoproteins from bloodstream forms of 13 cloned variants of Trypanosoma brucei was analyzed by gas-liquid chromatography. The glycoproteins contained from 6 to 17% carbohydrate by weight, and all contained the same 4 sugars: mannose, galactose, glucose, and glucosamine (probably as N-acetyl-glucosamine). The glycoprotein from variant 048, strain 427 contained (±20%) 11 mannose, 4 galactose, 4 glucose, and 5 glucosamine residues/mole of glycoprotein (molecular weight 65,000). Glucose was an integral component of the glycoproteins, not dissociable by sodium dodecyl sulphate, 8 M urea, or 1 M acetic acid. Some of the glucose was dissociated by trichloroacetic acid. Most of the glycoproteins formed precipitin bands with concanavalin A in Ouchterlony double diffusion, but none formed such bands with wheat germ agglutinin or Ricinus communis lectin (molecular weight 120,000).     

Carbohydrate composition of variant-specific surface antigen glycoproteins from Trypanosoma brucei

The carbohydrate of variant-specific surface antigen glycoproteins from bloodstream forms of 13 cloned variants of Trypanosoma brucei was analyzed by gas-liquid chromatography. The glycoproteins contained from 6 to 17% carbohydrate by weight, and all contained the same 4 sugars: mannose, galactose, glucose, and glucosamine (probably as N-acetylglucosamine). The glycoprotein from variant 048, strain 427 contained (+20%) 11 mannose, 4 galactose, 4 glucose, and 5 glucosamine residues/mole of glycoprotein (molecular weight 65,000). Glucose was an intergral component of the glycoproteins, not dissociable by sodium dodecyl sulphate, 8 M urea, or 1 M acetic acid. Some of the glucose was dissociated by trichloroacetic acid. Most of the glycoproteins formed precipitin with concanavalin A in Ouchterlony double diffusion, but none formed such bands with wheat germ agglutinin or Ricinus communis lectin (molecular weight 120, 000).     

Isolation of the major glycoprotein from plasma membranes of an ascites hepatoma AH 66.

Plasma membranes were isolated from AH 66 cells, some of which had been labeled with [14C]glucosamine, by the following procedure: homogenization of cells which had been hardened by treatment with Zn ions, fractionation of the homogenate by sucrose density gradient centrifugation and purification of the membranes by partition in an aqueous two-phase polymer system. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS) of the plasma membranes and subsequent staining of the gel for protein and carbohydrate, and determination of radioactivity on the gel eluates indicated the presence of at least 10 bands of glycoproteins. The major band contained 27% of the total radioactivity incorporated into the plasma membranes and was most heavily stained with the periodate-Schiff reagent. To isolate the major glycoprotein, the membranes were solubilized with 0.6 M lithium diiodosalicylate containing 0.5% Triton X-100, then the solution was treated with phenol. The major glycoprotein, obtained in the aqueous phase, was further purified mainly by repeated chromatographies on Sepharose 6B. The purified preparation was practically homogeneous on SDS-polyacrylamide gel electrophoresis, as judged by radioactivity determination and by carbohydrate staining, but contained small amounts of carbohydrate-free proteins. The major glycoprotein had an apparent molecular weight of 160,000, as determined by SDS-polyacrylamide gel electrophoresis. The final preparation contained about 44% carbohydrate on a weight basis, and the carbohydrate moiety was composed of glucosamine, galactosamine, galactose, mannose, fucose, and sialic acid. This composition indicates that the major glycoprotein contains both N- and O-glycosidically linked oligosaccharide moieties.     

Isolation and partial characterization of the major glycoproteins of horse and swine erythrocyte membranes

The major glycoproteins of horse and swine erythrocyte membranes were isolated and examined chemically and immunologically. The major glycoprotein of horse erythrocyte membranes had a molecular weight of 33 000 and consisted of 46.2% protein and 53.8% carbohydrate, of which 9.4% was hexose, 10.1% hexosamine and 33.7% sialic acid. This glycoprotein was associated with activity for the infectious mononucleosis heterophile antigen.There were two different major glycoproteins in swine erythrocyte membranes. One major glycoprotein had a molecular weight of 46 200 and consisted of 34.2% protein and 65.8% carbohydrate, of which 18% was hexose, 19% hexosamine and 27.2% sialic acid. This glycoprotein had phytohemagglutinin (Phaseolus vulgaris) binding activity. The other glycoprotein had a molecular weight of 29 000 and consisted of 50.4% protein and 49.6% carbohydrate, of which 6.4% was hexose, 7.0% hexosamine and 36.3% sialic acid. This glycoprotein had weak or absent phytohemagglutinin binding activity.     

SDS gel electrophoresis of proteins and glycoproteins from peritrophic membranes of some Diptera

Peritrophic membranes (PM) of larval and adult Calliphora erythrocephala and Sarcophaga barbata contain proteins and glycoproteins which were extracted by 2.5% SDS and 8 M urea from the matrix. The acid mucopolysaccharide moiety of PM which was demonstrated by the carbazole method remained in the insoluble resudues. After SDS electrophoresis the gels were counterstained with PAS and Coomassie blue; the carbohydrate and protein content of the bands were recorded by dual scanning. Besides molecular weight (MW) determination from the migration rate, the MW of some glycoprotein bands of PM were evaluated also from their retardation coefficients. The methods revealed different results indicating anomalous SDS binding and mobility of these glycoproteins in SDS electrophoresis.The glycoprotein patterns of larvae and of adults of Calliphora as well as of Sarcophaga differed markedly. PM of adults of both species contained only one carbohydrate fraction which migrated in the gel according to an apparent MW of about 200.000 daltons. PM of the larvae, however, showed a variety of bands in the range between 30.000 and 80.000 daltons which had binding capacities for the protein as well as for the carbohydrate stain. On the other hand, the patterns of pure protein bands were similar in the larval and in the adult stage. Obviously, the glycoprotein pattern of PM is altered during development according to special requirements. Also the similarities between both species in the larval and in the adult stage point to a special physiological function of the glycoprotein moiety.     

Isolation and characterization of a glycoprotein from human colostrum

A glycoprotein was isolated from the M-1 acid glycoprotein fraction of human colostrum. It had a molecular weight of 31200 and contained 27% galactose, 21.7% hexosamine, 8.0% fucose and 10.8% sialic acid by weight. The glycoprotein had no absorption maxima in the 240-300nm region, and was virtually free of ABH(O) and M and N blood-group activity. Alkaline borohydride cleavage of the glycoprotein resulted predominantly in the destruction of threonine and galactosamine.     

Isolation and characterization of two individual glycoprotein components from human milk-fat-globule membranes.

Two individual glycoprotein components from human milk-fat-globule membranes (MFGM) has been purified by selectively extracting the membrane glycoproteins followed by lectin affinity chromatography and gel filtration on Sephadex G-200 in the presence of protein-disaggregating agents. The purified glycoprotein components, termed 'epithelial-membrane glycoprotein' (EMGP-155 and EMGP-39) have estimated molecular weights of 155 000 and 39 000 respectively, and yield a single band under reducing conditions on sodium dodecyl sulphate/polyacrylamide gel. EMGP-155 and EMGP-39 contain 21.0% and 7.0% carbohydrate by weight, with fucose (13.5%, 12.4%), mannose (3.7%, 6.2%), galactose (28.5%, 22.6%), N-acetylglucosamine (17.8%, 7.4%) and sialic acid (36.4%, 51.4%) of the carbohydrate moiety respectively. For both the glycoprotein components, aspartic and glutamic acid and serine are the major amino acid residues.     

Magnetic-circular-dichroism studies of haem a and its derivatives.

1. The Thy-1 membrane glycoproteins from rat thymus and brain bound deoxycholate to 24% of their own weight as measured by equilibrium dialysis. The binding occurred co-operatively at the critical micelle concentration of deoxycholate, suggesting that the glycoproteins bind to a micelle, and not to the detergent monomer. 2. From sedimentation-equilibrium and deoxycholate-binding data the molecular weights of the glycoprotein monomers were calculated to be 18700 and 17500 for thymus and brain Thy-1 glycoprotein monomers were calculated to be 18700 and 17500 for thymus and brain Thy-1 glycoproteins respectively. The molecular weight of the polypeptide part of the glycoprotein is thus 12500. 3. In the absence of deoxycholate, brain or thymus Thy-1 glycoprotein formed large homogeneous complexes of mol. wt. 270000 or 300000 respectively. The sedimentation coefficient of these was 12.8 S. The complex was only partially dissociated by 4M-guanidinium chloride. 4. After cleavage of brain or thymus Thy-1 glycoprotein with CNBr, two peptides were clearly identified. They were linked by disulphide bonds and both contained carbohydrate. This cleavage suggests there is only one methionine residue per molecule, which is consistent with the above molecular weights and the known amino acid composition.     

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.     

Structural features of carbohydrate chains in human salivary mucins

• 1.1. The structure of carbohydrate chains in the low and high molecular weight mucus glycoprotein forms from submandibular-sublingual saliva of individuals with blood group B was investigated.
• 2.2. Alkaline borohydride reductive cleavage of the glycoproteins yielded in each case a population of neutral (55%) and acidic (45%) oligosaccharide alditols ranging in size from 3 to 16 sugar units.
• 3.3. The predominant neutral oligosaccharides in both glycoprotein forms consisted of 16 and 15 sugar units arranged in triantennary fashion, and carried blood group B and I antigenic determinants.
• 4.4. Three of the oligosaccharides in each glycoprotein contained sialic acid and ranged in size from 3 to 12 sugar units. In two oligosaccharides sialic acid was linked to C3 of galactose and in one to C6 of N-acetylgalactosamine. The sulfated oligosaccharide in both glycoproteins was identified as a pentasaccharide with the sulfate ester group at C6 of N-acetylglucosamine.
• 5.5. The results demonstrate that contrary to the earlier view the low and high molecular weight mucus glycoprotein forms of human saliva contain identical carbohydrate chains.

     

Studies on the uronic acid-containing glycoproteins of Fusarium sp. M7-1: I. Isolation and some properties of the glycoproteins.

An acidic heteropolysaccharide preparation derived from the mycelium of Fusarium sp. M7-1 was fractionated into two fractions, precipitable and nonprecipitable, by treatment with cetyltrimethylammonium bromide (Cetavlon). These two fractions were further purified to apparent homogeneity on ultracentrifugation by treatment with charcoal and gel filtration chromatographies. Two glycoproteins, precipitable GP I and nonprecipitable GP II, were obtained. The molecular weights of GP I and GP II were estimated to be about 8.8 x 10(4) and 3.7 x 10(4), respectively, on gel filtration chromatography. Both GP I and GP II contained a high proportion of serine and threonine. Treatment of GP I and GP II with alkaline solution resulted in an increase in absorbance at 240 nm. Alkaline borohydride treatment markedly decreased the number of seryl and threonyl residues and resulted in an increase in alanine and the formation of 2-aminobutyric acid. It also resulted in release of low and high molecular weight carbohydrate chains. From these results, we conclude that both GP I and GP II are glycoproteins with carbohydrate chains attached to the protein moiety through O-glycosidic linkages to the hydroxyl group of serine and/or threonine.     

Synthesis and secretion of colonic glycoproteins: Evidence for shedding in vivo of low molecular weight membrane components

In vivo glycoprotein synthesis and secretion was studied in rat colonic epithelial cells using precursor labelling with radiolabelled glucosamine. Sepharose 4B gel filtration of radiolabelled glycoproteins obtained from isolated colonic epithelial cells revealed two major fractions: (1) high molecular weight mucus in the excluded fraction and (2) lower molecular weight glycoproteins in the included volume. These glycoproteins were further fractionated by affinity chromatography on concanavalin A-Sepharose. The low molecular weight [³H]glucosamine-labelled glycoproteins contained a major subfraction which specifically adhered to concanavalin A, and could be eluted with 0.2 M α-methylmannoside. Fractionation of the concanavalin A-reactive glycoproteins on Sephadex G-100 revealed a major peak with a molecular weight of 15 000. In contrast, high molecular weight mucus glycoprotein did not adhere appreciably to concanavalin A-Sepharose. Perfusion experiments indicated that colonic secretions contained both mucus and concanavalin A-reactive glycoproteins. The major concanavalin A-reactive glycoprotein in the colonic perfusate was not derived from serum, but was released directly from the colonic membrane into the lumen.     

Characterization of the oligosaccharide units of the bovine erythrocyte membrane glycoprotein.

The major glycoprotein of the bovine erythrocyte membrane was purified by extraction of the ghosts with lithium 3,5-diiodosalicylate followed by phenol-water extraction and acidification. The glycoprotein contains 20% protein and 80% carbohydrate by weight and gives a single band on sodium dodecyl sulfate-polyacrylamide gels with an estimated molecular weight of 230000 daltons. The carbohydrate composition of the glycoprotein was determined to be (in residues relative to sialic acid): sialic acid, 1.0; fucose, less than 0.01; mannose, 0.1; galactose, 3.3; N-acetylgalactosamine, 0.9; and N-acetylglucosamine, 2.4. Pronase digestion of the isolated glycoprotein followed by Sephadex G-75 gel filtration resulted in the separation of a small pool of glycopeptides (pool III), which included all of the mannose-containing glycopeptides, from the bulk of the glycopeptide material which was in the void fractions of the column (pool I). Alkaline borohydride treatment released over 95% of the oligosaccharide units in pool I and approximately 30% of the oligosaccharide units in pool III. These oligosaccharides were isolated by gel filtration and ion-exchange chromatography. The oligosaccharides released from pool I had molecular weights of 1100-1400 daltons and contained sialic acid, galactose, and N-acetylglucosamine in molar ratios of 0.5-1:3:2 as well as a partial residue of N-acetylgalactosaminitol. The oligosaccharides released from pool III by alkali had molecular weights of 1300-1600 daltons and contained sialic acid, galactose, N-acetylglucosamine, N-acetylgalactosamine and N-ACETYLgalactosaminitol in molar ratios of 1-2:2:1:1:1. These data indicate that the majority of the oligosaccharide units of the bovine erythrocyte glycoprotein are linked O-glycosidically to the peptide backbone of the molecule.     

Interaction of a hydroxyproline-rich glycoprotein from tobacco callus with potential pathogens

A hydroxyproline-rich glycoprotein was isolated from tobacco (Nicotiana tabacum L.) callus tissue cultures by an acidic-ethanol extraction procedure and purified to about 95% homogeneity by ion exchange chromatography on carboxymethyl cellulose. This glycoprotein agglutinated cells of an avirulent strain (B-1) of the bacterial pathogen Pseudomonas solanacearum but not its parental, virulent isolate (K-60). Bacterial lipopolysaccharide (from K-60 strain) inhibited this agglutination. The tobacco glycoprotein also agglutinated zoospores of both compatible and incompatible races of Phytophthora parasitica var. nicotianae. Although 34 potential haptens were tested, no low-molecular-weight carbohydrate that inhibited bacterial or fungal agglutination was found. The agglutination activity of the tobacco glycoprotein was sensitive to pronase and sodium periodate. The apparent molecular weight of the glycoprotein was 120,000. The protein moiety was basic (12% lysine and 5% histidine) and contained 38% hydroxyproline. The carbohydrate moiety comprised 26% (by weight) of the glycoprotein, and contained 87% arabinose, 8% galactose, and 5% glucose. The glycoprotein labeled with fluorescein isothiocyanate bound significantly better to the avirulent isolate (B-1) of P. solanacearum than to the virulent strain (K-60). Binding to the avirulent cells was inhibited by incubation in a higher ionic strength medium (e.g. 0.2 m NaCl). The labeled glycoprotein also bound to cystospores and mycelia of both races of P. parasitica var. nicotianae. This fungal-glycoprotein interaction was inhibited by the lipopolysaccharide from strain K-60 and by higher ionic strength conditions.     

Isolation and characterization of a major glycoprotein from milk-fat-globule membrane of human breast milk.

A major periodate--Schiff-positive component from milk-fat-globule membrane of human breast milk has been purified by selectively extracting the membrane glycoproteins, followed by lectin affinity chromatography and gel filtration on Sephadex G-200 in the presence of protein-dissociating agents. The purified glycoprotein, termed epithelial membrane glycoprotein (EMGP-70), has an estimated mol.wt. of 70 000 and yields a single band under reducing conditions on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. The glycoprotein contains 13.5% carbohydrate by weight, with fucose, mannose, galactose, N-acetylglucosamine and sialic acid 17.2, 17.0, 21.1, 7.9 and 36.6% respectively of the carbohydrate moiety. Aspartic and glutamic acid and serine are the major amino acid residues.     

Isolation and characterization of rare earth element-binding protein in roots of maize

Rare earth element-binding protein was isolated from maize, which was grown under greenhouse conditions and characterized in terms of molecular weight, amino acid composition, and ultraviolet absorption. The molecular weight of the maize protein was determined to be 183,000, with two distinct subunits of approximately molecular weights of 22,000 and 69,000, respectively. The protein is particularly rich in asparagine/aspartic acid, glutamine/glutamic acid, glycine, alanine, and leucine and contains 8.0% of covalently bound carbohydrate. The ultraviolet absorption of the protein is low at 280 nm and no change in the adsorption was observed with a change in pH. Compared to the unique features of the metallothioneins with a molecular weight of approximately 10,000, a high cysteine content of 30%, high absorption at 254 nm and a low absorption at 280 nm, and absorption change with pH, the REE-binding protein is unlikely to be plant metallothionein in nature. It was found that an almost twofold greater concentration was found for most of the REEs in the protein isolated from the maize with REE fertilizer use than that without REE fertilizer. This study suggests that the REE-binding protein is a glycoprotein and REEs can be firmly bound with the protein of maize roots.     

Human immunodeficiency virus type 1 envelope glycoprotein is modified by O-linked oligosaccharides.

The human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein has been shown to be extensively modified by N-linked glycosylation; however, the presence of O-linked carbohydrates on the glycoprotein has not been firmly established. We have found that enzymatic deglycosylation of the HIV-1 envelope glycoprotein with neuraminidase and O-glycosidase results in a decrease in the apparent molecular weight of the envelope glycoprotein. This result was observed in both vaccinia virus recombinant-derived envelope glycoproteins and glycoproteins derived from the IIIB, SG3, and HXB2, strains of HIV-1. The decrease in molecular weight was also observed when the envelope glycoprotein had been deglycosylated with N-glycanase F after treatment with neuraminidase and O-glycosidase, indicating that the decrease in apparent molecular weight was not attributable to the removal of N-linked carbohydrate. Treatment with neuraminidase, O-glycosidase, and N-glycanase F was found to be necessary to remove all radiolabel from [3H]glucosamine-labelled envelope glycoprotein, a result seen for both recombinant and HIV-1-derived envelope glycoprotein. [3H]glucosamine-labelled carbohydrates liberated by O-glycosidase treatment were separated by paper chromatography and were found to be of a size consistent with O-linked oligosaccharides. We, therefore, conclude that the HIV-1 envelope glycoprotein is modified by the addition of O-linked carbohydrates.     

Purification and characterization of the invertase from Schizosaccharomyces pombe. A comparative analysis with the invertase from Saccharomyces cerevisiae.

Invertase (EC 3.2.1.26) was purified to homogeneity from exponentially growing cells of Schizosaccharomyces pombe fully de-repressed for synthesis of the enzyme, and was shown to be a high-molecular-mass glycoprotein that can be dissociated in the presence of 8 M-urea/1% SDS into identical subunits with an apparent molecular mass of 205 kDa. The carbohydrate moiety, accounting for 67% of the total mass, is composed of equimolar amounts of mannose and galactose. There is a small amount of glucosamine, which is probably involved in the linkage to the protein moiety, since the enzyme is sensitive to treatment with endoglycosidase H. The composition of the carbohydrate moiety resembles that found in higher-eukaryotic glycoproteins and differs from glycoproteins found in Saccharomyces cerevisiae. The protein portion of each subunit is a polypeptide of molecular mass 60 kDa, very similar to the invertase of Sacch. cerevisiae. Both proteins cross-react with antibodies raised against the protein fractions of the other, indicating that the two enzymes are similar.     

Analysis of changes in a yolk glycoprotein complex in the developing sea urchin embryo

A sea urchin yolk glycoprotein complex (YGC) was isolated from several developmental stages by velocity centrifugation on sucrose gradients. The YGCs were analyzed by SDS-polyacrylamide gel electrophoresis to determine if the molecular composition of the YGC was changing during development. The mass of the YGC did not change with development. However, as development proceeded there were significant changes in the glycoprotein composition of the YGC isolated from either Lytechinus pictus or Strongylocentrotus purpuratus embryos. In both species the YGC isolated from eggs contained three major glycoproteins. The most abundant one had an apparent molecular weight of 190,000 and was designated GP-190. During development the three major egg YGC glycoproteins decreased in relative amounts as intermediate-molecular-weight glycoproteins increased. While these changes were detected in YGCs isolated from either species, the rate of change was much greater in S. purpuratus than in L. pictus. The most significant difference was observed in the rate of decrease in GP-190. In S. purpuratus, GP-190 showed a significant decrease by 8-10 hr postfertilization, while a similar decrease did not occur in L. pictus YGCs until 72 hr postfertilization. To determine how these changes were occurring, both amino acid and carbohydrate analyses were done on the YGC isolated from various stages. From examination of these data, it appeared that the molecular composition of the YGC was changing via very limited proteolysis. The intermediate and low-molecular-weight glycoproteins generated apparently remain assembled in the YGC, thus conserving its mass.     

Biochemical and immunological characterization and the synthesis of rat intestinal glycoproteins following the induction of rapid synchronous vitamin A deficiency

Glycoproteins and proteins were extracted from segments or scrapings of the intestine in tube-fed, vitamin-A-deficient and control rats on the eight day after withdrawal of retinoic acid from the diet by using either 1% sodium dodecyl sulfate (SDS) or aqueous 5 mM EDTA (pH 7.4). They were then fractionated on columns of Sepharose 4B. Water-soluble peak I material contained large (M_r > 10⁶; S₂₀ = 11.7) glycoprotein aggregates which were rich in hexose, fucose and sialic acid. These aggregates dissociated into several non-identical glycoprotein and protein subunits upon treatment with dithiothreitol. The protein matrix was rich in threonine, valine, proline, serine, glutamate and aspartate. Peak II consisted of smaller proteins and glycoproteins, the latter with much lower carbohydrate content. Some peak II glycoproteins also dissociated into subunits in the presence of dithiothreitol. Peak III consisted mainly of a heterogenous assortment of proteins, including some glycoproteins of low carbohydrate content. Antibodies either to peak II or to peak III reacted both with peaks II and III but not with peak I.The total weight, carbohydrate composition of glycoproteins and the ratio of carbohydrate to protein in the total extract or in each of the three fractions were not significantly affected in vitamin A deficiency despite decreased incorporation of all labeled precursors. Rather, the relatively lower incorporation (approx. 0.8) of radioactive sulfate, D-glucosamine and L-fucose into total SDS-soluble duodenal glycoproteins of vitamin-A-deficient rats could be explained on the basis of a reduced prevalence of goblet cells alone. In contrast, the relative incorporation rate of L-fucose into peak I, but not into peaks II and III, ranged from 0.25 to 0.45, less than expected on the basis of fewer goblet cells alone. The incorporation of radioactive threonine into all protein fractions was reduced to 60% of normal in vitamin A deficiency. Thus, the well established observation that intestinal tissue of vitamin-A-deficient rats synthesizes high molecular weight glycoproteins poorly might be due to several interacting factors: (1) a reduced prevalence of goblet cells, (2) a lower rate of protein synthesis, (3) a lack of retinyl phosphate for the formation of mannosyl or other carbohydrate derivatives, and (4) secondary, and as yet undefined, cellular changes which preferentially reduce the rate of synthesis of high molecular weight fucose- and sialic-acid-enriched glycoproteins.