Glycoprotein synthesis in the adult rat pancreas: II. Characterization of Golgi-rich fractions

Golgi-rich fractions were prepared from homogenates of adult rat pancreas by discontinuous gradient centrifugation. These fractions were characterized by stacks of cisternae associated with large, irregular vesicles and were relatively free of rough microsomes, mitochondria, and zymogen granules. The Golgi-rich fractions contained 50% of the UDP-galactose: glycoprotein galactosyltransferase activity; the specific activity was 12-fold greater than the homogenate. Such fractions represented < 19% of thiamine pyrophosphatase, uridine diphosphatase, adenosine diphosphatase, and Mg²⁺-adenosine triphosphatase. Zymogen granules and the Golgi-rich fractions were extracted with 0.2 m NaHCO3, pH 8.2, and the membranes were isolated by centrifugation. The glycoprotein galactosyltransferase could not be detected in granule membranes, while the specific activity in Golgi membranes was 25-fold greater than the homogenate.At least 35 polypeptide species were detected in Golgi membranes by polyacrylamide gel electrophoresis in 1% sodium dodecylsulfate. These ranged in molecular weight from 12,000 to <160,000. There were only minor differences between Golgi membranes and smooth microsomal membrane. In contrast, zymogen granule membranes contained fewer polypeptides. A major polypeptide, which represented 30–40% of the granule membrane profile, accounted for less than 3% of the polypeptides of Golgi membranes or smooth microsomal membranes.     

Association of the Golgi UDP-galactose transporter with UDP-galactose:ceramide galactosyltransferase allows UDP-galactose import in the endoplasmic reticulum

UDP-galactose reaches the Golgi lumen through the UDP-galactose transporter (UGT) and is used for the galactosylation of proteins and lipids. Ceramides and diglycerides are galactosylated within the endoplasmic reticulum by the UDP-galactose:ceramide galactosyltransferase. It is not known how UDP-galactose is transported from the cytosol into the endoplasmic reticulum. We transfected ceramide galactosyltransferase cDNA into CHOlec8 cells, which have a defective UGT and no endogenous ceramide galactosyltransferase. Cotransfection with the human UGT1 greatly stimulated synthesis of lactosylceramide in the Golgi and of galactosylceramide in the endoplasmic reticulum. UDP-galactose was directly imported into the endoplasmic reticulum because transfection with UGT significantly enhanced synthesis of galactosylceramide in endoplasmic reticulum membranes. Subcellular fractionation and double label immunofluorescence microscopy showed that a sizeable fraction of ectopically expressed UGT and ceramide galactosyltransferase resided in the endoplasmic reticulum of CHOlec8 cells. The same was observed when UGT was expressed in human intestinal cells that have an endogenous ceramide galactosyltransferase. In contrast, in CHOlec8 singly transfected with UGT 1, the transporter localized exclusively to the Golgi complex. UGT and ceramide galactosyltransferase were entirely detergent soluble and form a complex because they could be coimmunoprecipitated. We conclude that the ceramide galactosyltransferase ensures a supply of UDP-galactose in the endoplasmic reticulum lumen by retaining UGT in a molecular complex.     

The effect of wheat germ agglutinin on sialyl and galactosyltransferases of rat liver Golgi membranes.

The sialyltransferase and galactosyltransferase activities of the Golgi-rich fraction from rat liver were enhanced by the binding of wheat germ agglutinin (WGA). The sialytransferase was more sensitive than the galactosyltransferase to the WGA. Maximal stimulation of the galactosyltransferase activity resulted from the binding of 60--80 micrograms WGA to the Golgi membrane, while only 40 micrograms of WGA produced a maximal enhancement in the sialyltransferase activity. Within 5 min of WGA binding, the Golgi sialytransferase activity was doubled. After the initial binding of WGA to the Golgi fraction, the galactosyltransferase activity was decreased by 30%. However, in 15 min the activity was doubled by the binding of WGA. The activities of both enzymes were further enhanced by incubation for up to 90 min. The stimulation of both sialyltransferase and galactosyltransferase activities by WGA was reversed by N-acetyl-D-glucosamine (GlcNAc), the specific inhibitor of agglutination by WGA. Complete reversal of the enhanced activity was observed after 20--30 min in the presence of 1 micromol GlcNAc. The association constant for the binding of WGA to the Golgi membranes was calculated to be 4.16 X 10(-6) M from a Steck-Wallach plot. The 'n' value or mean binding sites was calculated as 5.26 X 10(-5) M/mg of Golgi membrane protein.     

Golgi and endoplasmic reticulum functions take place in different subcellular compartments of Entamoeba histolytica

Entamoeba histolytica is a protozoan parasite that causes dysentery in developing countries of Africa, Asia, and Latin America. The lack of a defined Golgi apparatus in E. histolytica as well as in other protists led to the hypothesis that they had evolved prior to the acquisition of such organelle even though glycoproteins, glycolipids, and antigens have been detected, the latter of which react with antibodies against Golgi apparatus proteins of higher eukaryotes. We here provide direct evidence for Golgi apparatus-like functions in E. histolytica as well as for components of glycoprotein folding quality control. Using a combination of bioinformatic, cell biological, and biochemical approaches we have (a) cloned and expressed the E. histolytica UDP-galactose transporter in Saccharomyces cerevisiae; its K(m) for UDP-galactose is 2.9 microm; (b) characterized vesicles in an extract of the above protist, which transport UDP-galactose into their lumen with a K(m) of 2.7 microm;(c) detected galactosyltransferase activity(ies) in the lumen of the above vesicles with the K(m) for UDP-galactose, using endogenous acceptors, being 93 microm;(d) measured latent apyrase activities in the above vesicles, suggesting they are in the lumen; (e) characterized UDP-glucose transport activities in Golgi apparatus and endoplasmic reticulum-like vesicles with K(m)s for UDP-glucose of approximately 2-4 microm. Although the endoplasmic reticulum-like fraction showed UDP-glucose: glycoprotein glucosyltransferase activity, the Golgi apparatus-like fraction did not. This fraction contained other glucosyltransferases. Together, these studies demonstrate that E. histolytica has different vesicles that play a role in protein glycosylation and folding quality control, analogous to the above organellar functions of higher eukaryotes.     

Transport of UDP-galactose in plants. Identification and functional characterization of AtUTr1, an Arabidopsis thaliana UDP-galactos/UDP-glucose transporter

The synthesis of non-cellulosic polysaccharides and glycoproteins in the plant cell Golgi apparatus requires UDP-galactose as substrate. The topology of these reactions is not known, although the orientation of a plant galactosyltransferase involved in the biosynthesis of galactomannans in fenugreek is consistent with a requirement for UDP-galactose in the lumen of the Golgi cisternae. Here we provide evidence that sealed, right-side-out Golgi vesicles isolated from pea stems transport UDP-galactose into their lumen and transfer galactose, likely to polysaccharides and other acceptors. In addition, we identified and cloned AtUTr1, a gene from Arabidopsis thaliana that encodes a multitransmembrane hydrophobic protein similar to nucleotide sugar transporters. Northern analysis showed that AtUTr1 is indeed expressed in Arabidopsis. AtUTr1 is able to complement the phenotype of MDCK ricin-resistant cells; a mammalian cell line deficient in transport of UDP-galactose into the Golgi. In vitro assays using a Golgi-enriched vesicle fraction obtained from Saccharomyces cerevisiae expressing AtUTr1-MycHis is able to transport UDP-galactose but also UDP-glucose. AtUTr1- MycHis does not transport GDP-mannose, GDP-fucose, CMP-sialic acid, UDP-glucuronic acid, or UDP-xylose when expressed in S. cerevisiae. AtUTr1 is the first transporter described that is able to transport UDP-galactose and UDP-glucose. Thus AtUTr1 may play an important role in the synthesis of glycoconjugates in Arabidopsis that contain galactose and glucose.     

Rat liver Golgi galactosyltransferases. Distinct enzymes for glycolipid and glycoprotein acceptor substrates.

Two enzymes that catalyse the transfer of galactose from UDP-galactose to GM2 ganglioside were partially purified from rat liver Golgi membranes. These preparations, designated enzyme I (basic) and enzyme II (acidic), utilized as acceptors GM2 ganglioside and asialo GM2 ganglioside as well as ovalbumin, desialodegalactofetuin, desialodegalacto-orosomucoid, desialo bovine submaxillary mucin and GM2 oligosaccharide. Enzyme II catalysed disaccharide synthesis in the presence of the monosaccharide acceptors N-acetylglucosamine and N-acetylgalactosamine. The affinity adsorbent alpha-lactalbumin-agarose, which did not retard GM2 ganglioside galactosyltransferase, was used to remove most or all of galactosyltransferase activity towards glycoprotein and monosaccharide acceptors from the extracted Golgi preparation. After treatment of the extracted Golgi preparation with alpha-lactalbumin-agarose, enzyme I and enzyme II GM2 ganglioside galactosyltransferase activities, prepared by using DEAE-Sepharose chromatography, were distinguishable from transferase activity towards GM2 oligosaccharide and glycoproteins by the criterion of thermolability. This residual galactosyltransferase activity towards glycoprotein substrates was also shown to be distinct from GM2 ganglioside galactosyltransferase in both enzyme preparations I and II by the absence of competition between the two acceptor substrates. The two types of transferase activities could be further distinguished by their response to the presence of the protein effector alpha-lactalbumin. GM2 ganglioside galactosyltransferase was stimulated in the presence of alpha-lactalbumin, whereas the transferase activity towards desialodegalactofetuin was inhibited in the presence of this protein. The results of purification studies, comparison of thermolability properties and competition analysis suggested the presence of a minimum of five galactosyltransferase species in the Golgi extract. Five peaks of galactosyltransferase activity were resolved by isoelectric focusing. Two of these peaks (pI 8.6 and 6.3) catalysed transfer of galactose to GM2 ganglioside, and three peaks (pI 8.1, 6.8 and 6.3) catalysed transfer to glycoprotein acceptors.     

The activity of Golgi-membrane galactosyltransferase in the liver of streptozotocin-diabetic rats.

The Golgi-rich membrane fraction isolated from streptozotocin-diabetic rat liver had a lower protein content than the corresponding fraction from normal liver. Its UDPgalactose-N-acetylglucosamine galactosyltransferase activity calculated per 1 g of liver or whole liver was decreased. The electron-microscopic examination of the negatively stained fraction revealed morphological changes. The morphology of the Golgi complex in thin sections of diabetic liver was also changed.     

A possible role of Golgi membrane-associated galactosyltransferase in the formation of zymogen granule glycoproteins

A galactosyltransferase activity in smooth microsomes and Golgi membrane-rich fractions from rat pancreas glycosylated endogenous acceptors during incubation with UDP-[¹⁴C]galactose in the absence of exogenous glycoproteins. To evaluate the role of this activity in secretion, the endogenous products were partially characterized. Galactose-labeled fractions were sequentially extracted in 0.2 m NaHCO₃ and 0.25 m NaBr to prepare membranes and soluble acceptors. Bound radioactivity was equally distributed between these two fractions. Analysis by polyacrylamide gel electrophoresis in sodium dodecyl sulfate indicated that the particulate galactose-labeled polypeptides were distinct from the soluble galactose acceptors. Rabbit antisera against highly purified zymogen granule membranes precipitated approximately 40% of the radioactivity of the particulate fraction when solubilized in nonionic detergents. In polyacrylamide gels, the galactose-labeled species of the immunoprecipitate migrated with zymogen granule membrane glycoproteins. Rabbit antisera against secretory proteins cross-reacted with less than 5% of the galactose-labeled soluble acceptors. Mature zymogen granule membranes neither contained detectable galactosyltransferase activity nor served as galactosyltransferase acceptors. These results suggest that galactosyltransferase activity associated with membranes derived from the Golgi complex glycosylated zymogen granule membrane precursors. Analysis of [¹⁴C]galactolipids did not implicate lipid intermediates in this process.     

Localization of cerebroside-sulfotransferase activity in the Golgi apparatus of rat kidney

A Golgi-rich fraction that contains both uridine diphosphogalactose: N-acetylglucosamine galactosyltransferase activity and 3′-phosphoadenosine-5′-phosphosulfate:cerebroside sulfotransferase activity has been isolated from rat kidney. Both activities are increased about 80-fold in the Golgi fraction compared to the homogenate. Little or no galactosyltransferase or sulfotransferase activity was found in purified nuclei, mitochondria, rough endoplasmic reticulum, plasma membranes and supernatant. The results indicate that both galactosyltransferase and sulfotransferase are localized in Golgi apparatus from rat kidney. This is the first evidence that Golgi apparatus functions to modify a lipid component of the cell.     

Topology of UDP-galactose cleavage in relation to N-acetyl-lactosamine formation in Golgi vesicles. Translocation of activated galactose.

UDP-galactose appears to be produced on one side of a membrane barrier, opposite the galactosyltransferases that use it as a sugar donor. The translocation of activated galactose across membranes was studied in rat submaxillary-gland microsomal vesicles and in rat liver Golgi vesicles. When these intact vesicles containing the acceptor, N-acetylglucosamine, were incubated in the presence of UDP-galactose and two inhibitors of galactosyltransferase activity, the product, N-acetyl-lactosamine, formed within the vesicles. Thus at least the galactose moiety of UDP-galactose crossed the membranes. When intact Golgi vesicles were incubated with UDP-galactose labelled in both the uridine and the galactose moieties, labelled N-acetyllactosamine was again produced in the vesicles, but less than stoichiometric amounts of the uridine label was found there. Calculation of internal and external concentrations of UMP, a major product released from the cleaved uridine moiety, showed that the vesicles were actually enriched in UMP. When free UMP was incubated with the vesicles, this enrichment did not occur. This result was direct evidence for facilitated transport of UDP-galactose into the Golgi for use by galactosyltransferase.     

A galactosyltransferase from the fission yeast Schizosaccharomyces pombe

A membrane-associated galactosyltransferase has been purified to homogeneity from the fission yeast, Schizosaccharomyces pombe. The enzyme has a molecular weight of 61,000 and is capable of transfering galactose from UDP-galactose (UDP-Gal) to a variety of mannose-based acceptors to form an alpha-1,2 galactosyl mannoside linkage. Immunofluorescence localization of the protein is consistent with the presence of the enzyme in the Golgi apparatus of S. pombe. This, together with the presence of terminal, alpha-linked galactose on the N- linked oligosaccharides of S. pombe secretory proteins, suggests that the galactosyltransferase is an enzyme involved in the processing of glycoproteins transported through the Golgi apparatus in fission yeast.     

The cytoplasmic droplet of rat epididymal spermatozoa contains saccular elements with Golgi characteristics

The cytoplasmic droplet of epididymal spermatozoa is a small localized outpouching of cytoplasm of the tail of unknown significance. EM revealed flattened saccular elements as the near exclusive membranous component of the droplet. Light and electron microscopic immunolabeling for Golgi/TGN markers showed these saccules to be reactive for antibodies to TGN38, protein affinity-purified alpha 2,6 sialyltransferase, and anti-human beta 1,4 galactosyltransferase. The saccules were isolated by subcellular fractionation and antibodies raised against this fraction immunolabeled the saccules of the droplet in situ as well as the Golgi region of somatic epithelial cells lining the epididymis. The isolated droplet fraction was enriched in galactosyltransferase and sialyltransferase activities, and endogenous glycosylation assays identified the modification of several endogenous glycopeptides. EM lectin staining in situ demonstrated galactose and N- acetyl galactosamine constituents in the saccules. Endocytic studies with cationic and anionic ferritin as well as HRP failed to identify the saccules as components of the endocytic apparatus. Epididymal spermatozoa were devoid of markers for the ER as well as the Golgi- associated coatamer protein beta-COP. It is therefore unlikely that the saccular elements of the droplet participate in vesicular protein transport. However, the identification of Golgi/TGN glycosylating activities in the saccules may be related to plasma membrane modifications which occur during epididymal sperm maturation.     

GOLGI FRACTIONS PREPARED FROM RAT LIVER HOMOGENATES : II. Biochemical Characterization

The three Golgi fractions isolated from rat liver homogenates by the procedure given in the companion paper account for 6–7% of the protein of the total microsomal fraction used as starting preparation. The lightest, most homogeneous Golgi fraction (GF₁) lacks typical "microsomal" activities, e.g., glucose-6-phosphatase, NADPH-cytochrome c-reductase, and cytochrome P-450. The heaviest, most heterogeneous fraction (GF₃) is contaminated by endoplasmic reticulum membranes to the extent of ~15% of its protein. The three fractions taken together account for nearly all the UDP-galactose: N-acetyl-glucosamine galactosyltransferase of the parent microsomal fraction, and for ~70% of the activity of the original homogenate. Omission of the ethanol treatment of the animals reduces the recovery by half. The transferase activity is associated with the membranes of the Golgi elements, not with their content. Galactose is transferred not only to N-acetyl-glucosamine but also to an unidentified lipid-soluble component.     

Xylosylation and glucuronosylation reactions in rat liver Golgi apparatus and endoplasmic reticulum

We have studied in rat liver the subcellular sites and topography of xylosylation and galactosylation reactions occurring in the biosynthesis of the D-glucuronic acid-galactose-galactose-D-xylose linkage region of proteoglycans and of glucuronosylation reactions involved in both glycosaminoglycan biosynthesis and bile acid and bilirubin conjugation. The specific translocation rate of UDP-xylose into sealed, "right-side-out" vesicles from the Golgi apparatus was 2-5-fold higher than into sealed right-side-out vesicles from the rough endoplasmic reticulum (RER). Using the above vesicle preparations, we only detected endogenous acceptors for xylosylation in the Golgi apparatus-rich fraction. The specific activity of xylosyltransferase (using silk fibroin as exogenous acceptor) was 50-100-fold higher in Golgi apparatus membranes than in those from the RER. Previous studies had shown that UDP-galactose is translocated solely into vesicles from the Golgi apparatus. In these studies, we found the specific activity of galactosyltransferase I to be 40-140-fold higher in membranes from the Golgi apparatus than in those from the RER. The specific translocation rate of UDP-D-glucuronic acid into vesicles from the Golgi apparatus was 10-fold higher than into those from the RER, whereas the specific activity of glucuronosyltransferase (using chondroitin nonasaccharide as exogenous acceptor) was 12-30-fold higher in Golgi apparatus membranes than in those from the RER. Together, the above results strongly suggest that, in rat liver, the biosynthesis of the above-described proteoglycan linkage region occurs in the Golgi apparatus. The specific activity of glucuronosyltransferase, using bile acids and bilirubin as exogenous acceptor, was 10-25-fold higher in RER membranes than those from the Golgi apparatus. This suggests that transport of UDP-D-glucuronic acid into the RER lumen is not required for such reactions.     

Identification of a high affinity binding protein for the regulatory subunit RII beta of cAMP-dependent protein kinase in Golgi enriched membranes of human lymphoblasts.

Immunocytochemical evidence of an association between the regulatory subunit RII of the cAMP-dependent protein kinase (cAMP-PK) and the Golgi apparatus in several cell types has been reported. In order to identify endogenous Golgi proteins binding RII, a fraction enriched in Golgi vesicles was isolated from human lymphoblasts. Only the RII beta isoform was detected in the Golgi-rich fraction, although RII alpha has also been found to be present in these cells. A 85 kDa RII-binding protein was identified in Golgi vesicles using a [32P]RII overlay of Western blots. The existence of an endogenous RII beta-p85 complex in isolated Golgi vesicles was demonstrated by two independent means: (i) co-immunoprecipitation of both proteins under non-denaturing conditions with an antibody against RII beta and (ii) co-purification of RII beta-p85 complexes on a cAMP-analogue affinity column. p85 was phosphorylated by both endogenous and purified catalytic subunits of cAMP-pKII. Extraction experiments and protease protection experiments indicated that p85 is an integral membrane protein although it partitioned atypically during Triton X-114 phase separation. We propose that p85 anchors RII beta to the Golgi apparatus of human lymphoblasts and thereby defines the Golgi substrate targets most accessible to phosphorylation by C subunit. This mechanism may be relevant to the regulation of processes involving the Golgi apparatus itself, such as membrane traffic and secretion, but also relevant to nearby nuclear events dependent on C subunit.     

A kinetic comparison of partially purified rat liver Golgi and rat serum galactosyltransferases.

UDP-galactose: N-acetylglucosamine beta-1,4-galactosyltransferase was partially purified from rat liver Golgi membranes and rat serum. The kinetic parameters of the two enzymes isolated by affinity chromatography were compared with each other and with those for commercial bovine milk galactosyltransferase. When N-acetyl-glucosamine was the acceptor the Km values for UDP-galactose were 65,52 and 43 microM for the rat liver Golgi, rat serum and bovine milk enzymes respectively. The Km values for N-acetylglucosamine were 0.33, 1.49 and 0.5 mM for the three enzymes respectively. The Km values for UDP-galactose, with glucose as acceptor in the presence of 1 mg of alpha-lactalbumin, were 23, 9.0 and 60 microM for the three enzymes respectively, and the Km values for glucose were 2.3, 1.8 and 2.0 mM respectively. The effects of alpha-lactalbumin in both the lactosamine synthetase and lactose synthetase reactions were similar. The activation energies were 94.0 kJ/mol (22.5 kcal/mol) and 96.0 kJ/mol (22.9 kcal/mol) for the Golgi and serum enzymes respectively. Although some differences in Km values were observed between the rat liver Golgi and serum enzymes, the values obtained suggest a high degree of similarity between the kinetic properties of the three galactosyltransferases.     

Ganglioside biosynthesis in rat liver. Characterization of UDP-N-acetylgalactosamine -- GM3 acetylgalactosaminyltransferase

UDP-N-acetylgalactosamine--GM3 acetylgalactosaminyltransferase (GM2-synthase) was studied in a Golgi-rich fraction from rat liver. Activity in a cell-free system required the presence of detergents; octyl glucoside was found to be the most effective in stimulating the enzyme. Optimal activity of GM2-synthase was obtained at pH 7.2, in the presence of 0.8% octyl glucoside, 10 mM Mn2+ and 5 mM CDP-choline. The latter was used to counteract the rapid sugar nucleotide hydrolysis caused by a nucleotide pyrophosphatase activity in the Golgi fraction. The apparent Km values for UDP-N-acetylgalactosamine and added GM3 were 0.035 mM and 0.1 mM, respectively. Different results were obtained if endogenous GM3 only was used as the glycolipid acceptor. In this case, the apparent Km value for UDP-N-acetylgalactosamine was 0.18 mM and Co2+ and Fe2+ exceeded Mn2+ in activating GM2-synthase. Under optimal assay conditions and in the presence of added GM3 and 5 mM CDP-choline, the specific activity of the enriched Golgi fraction was measured to be 25-30 nmol X mg protein-1 X h-1; with endogenous GM3 as the sole glycolipid acceptor, V was calculated to be 9 nmol X mg protein-1 X h-1.     

Similarities of the Golgi apparatus membrane and the plasma membrane in rat liver cells.

A Golgi apparatus-rich fraction and a plasma membrane-rich fraction were isolated from a common homogenate of rat liver. Their respective buovant densities, appearances in the electron microscope and 5'-nucleotidase and UDP-galactose ovalbumin galactosyltransferase activities were in accord with published data on separately isolated Golgi apparatus-rich and plasma membrane-rich fractions. Contamination by endoplasmic reticulum and mitochondria was low. Gel electrophoresis of the membrane proteins of the Golgi apparatus-rich and plasma membrane-rich fractions (separately and mixed) showed a close similarity. After Neville's demonstration that electrophoretic patterns of membrane protein subunits from different subcellular fractions are easily distinguishable, the present work demonstrates an unusually close relationship between the Golgi apparatus membrane and the cell membrane. It is possible that membrane similarity may be mediated by the transfer of membrane-bound vesicles from the Golgi apparatus to the cell membrane.     

Ethanol-induced alterations of plasma membrane assembly in the liver

The effects of acute ethanol administration on the assembly of glycoproteins into the hepatic plasma membrane were studied in the rat. When [14C]fucose and N-acetyl[3H]mannosamine, a sialic acid precursor, were injected following an acute dose of ethanol, the incorporation of these precursors into the total pool of membrane glycoproteins was minimally affected. This finding indicated that ethanol treatment did not appreciably alter the glycosylation of proteins in the Golgi apparatus. However, the assembly of labeled fucoproteins and sialoproteins into the plasma membrane was markedly inhibited in the ethanol-treated animals. This inhibition of plasmalemmal glycoprotein assembly was accompanied by a corresponding accumulation of labeled glycoproteins in the cytosolic fraction of the hepatocyte. The content of labeled glycoproteins in the Golgi complex was not significantly altered by ethanol treatment. These results indicate that ethanol administration impairs the late stages of hepatic plasma membrane assembly and further suggest that ethanol administration interferes with the flow of membrane components from the Golgi apparatus to the surface membrane.     

Interaction of the retinol-cellular retinol-binding protein complex in the Golgi apparatus of mucosa cells from the chicken glandular stomach

A Golgi-rich fraction has been isolated from the chicken glandular stomach mucosa cells and characterized. Interaction of the [3H]retinol--cellular retinol-binding protein complex with Golgi-rich fraction is shown. The uptake process is specific and saturable. Free retinol does not penetrate to a Golgi-rich fraction. An assumption is advanced that retinol-binding protein is involved in the transport of retinol to various cell particles, in particular, to the Golgi apparatus.