Differentiation of Endoplasmic Reticulum in Hepatocytes

Leskes, A.; Siekevitz, Philip; Palade, George E.

doi:10.1083/jcb.49.2.264

Cited by 284 publications

(106 citation statements)

References 42 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Thus, the glucose-6-phosphate-accessible space appears to constitute only a fraction of the total water space of microsomes, which can theoretically be explained by a steady-state partial equilibration of glucose-6-phosphate across the microsomal membrane or/and by uneven distribution of the glucose-6-phosphatase system in microsomal vesicles. The latter possibility is not entirely consistent, however, with cytochemical ultrastructural evidence for a widespread distribution of glucose-6-phosphatase enzyme activity within liver endoplasmic reticulum in situ (7). In addition, liver microsomal preparations may well contain a (small) proportion of vesicles from membranes other than endoplasmic reticulum and lacking glucose-6-phosphate transporters.…”

Section: Discussionmentioning

confidence: 67%

“…de Duve et al (3), which mainly derives from the endoplasmic reticulum (ER) membranes (4). The latency of its activity, discovered in early studies (5,6), together with histochemical studies (7) indicated the compartmentation of the enzyme in the ER lumen. Consistent with this, more recent sequence information (8,9) revealed that mammalian glucose-6-phosphatases contain the carboxyl-terminal two-lysine retention motif by which transmembrane proteins are retained in the ER by retrieval from the Golgi (10,11).…”

mentioning

confidence: 99%

See 1 more Smart Citation

Demonstration of a Metabolically Active Glucose-6-phosphate Pool in the Lumen of Liver Microsomal Vesicles

Bánhegyi

Marcolongo

Fulceri

et al. 1997

Journal of Biological Chemistry

View full text Add to dashboard Cite

Glucose-6-phosphate transport was investigated in rat or human liver microsomal vesicles using rapid filtration and light-scattering methods. Upon addition of glucose-6-phosphate, rat liver microsomes accumulated the radioactive tracer, reaching a steady-state level of uptake. In this phase, the majority of the accumulated tracer was glucose, but a significant intraluminal glucose-6-phosphate pool could also be observed. The extent of the intravesicular glucose pool was proportional with glucose-6-phosphatase activity. The relative size of the intravesicular glucose-6-phosphate pool (irrespective of the concentration of the extravesicular concentration of added glucose-6-phosphate) expressed as the apparent intravesicular space of the hexose phosphate was inversely dependent on glucose-6-phosphatase activity. The increase of hydrolysis by elevating the extravesicular glucose-6-phosphate concentration or temperature resulted in lower apparent intravesicular glucose-6-phosphate spaces and, thus, in a higher transmembrane gradient of glucose-6-phosphate concentrations. In contrast, inhibition of glucose-6-phosphate hydrolysis by vanadate, inactivation of glucose-6-phosphatase by acidic pH, or genetically determined low or absent glucose-6-phosphatase activity in human hepatic microsomes of patients suffering from glycogen storage disease type 1a led to relatively high intravesicular glucose-6-phosphate levels. Glucose-6-phosphate transport investigated by light-scattering technique resulted in similar traces in control and vanadate-treated rat microsomes as well as in microsomes from human patients with glycogen storage disease type 1a. It is concluded that liver microsomes take up glucose-6-phosphate, constituting a pool directly accessible to intraluminal glucose-6-phosphatase activity. In addition, normal glucose-6-phosphate uptake can take place in the absence of the glucose-6-phosphatase enzyme protein, confirming the existence of separate transport proteins.

show abstract

Section: Discussionmentioning

confidence: 67%

mentioning

confidence: 99%

Demonstration of a Metabolically Active Glucose-6-phosphate Pool in the Lumen of Liver Microsomal Vesicles

Bánhegyi

Marcolongo

Fulceri

et al. 1997

Journal of Biological Chemistry

View full text Add to dashboard Cite

show abstract

“…A blank containing the sample but no AMP was run for each assay. 1 U of enzyme was defined as the activity which releases 1 tzmol of phosphate as Pl per hour at 37~ G6Pase activity was determined using the procedure described by De Duve et al (11) and Swanson (52), with the slight modification introduced by Leskes et al (28). Samples were incubated for 20 min at 37~ and the reaction was stopped by the addition of 15% TCA; two blanks for each sample were always included: one to which TCA was added at zero time, and one from which G6P was omitted.…”

Section: Enzymatic Assaysmentioning

confidence: 99%

Spatial orientation of glycoproteins in membranes of rat liver rough microsomes. II. Transmembrane disposition and characterization of glycoproteins.

Boulan¹,

Sabatini²,

Pereyra³

et al. 1978

The Journal of Cell Biology

View full text Add to dashboard Cite

Rat liver microsomal glycoproteins were purified by affinity chromatography on concanavalin A Sepharose columns from membrane and content fractions, separated from rough microsomes (RM) treated with low concentrations of deoxycholate (DOC). All periodic acid-Schiff (PAS)-positive glycoproteins of RM showed affinity for concanavalin A Sepharose; even after sodium dodecyl sulfate (SDS) acrylamide gel electrophoresis, most of the microsomal glycoproteins bound [lzsI]concanavalin A added to the gels, as detected by autoradiography. Two distinct sets of glycoproteins are present in the membrane and content fractions derived from RM. SDS acrylamide gel electrophoresis showed that RM membranes contain 15-20 glycoproteins (15-22% of the total microsomal protein) which range in apparent mol wt from 23,000 to 240,000 daltons. A smaller set of glycoproteins (five to seven polypeptides), with apparent mol wt between 60,000 and 200,000 daltons, was present in the microsomal content fraction.The disposition of the membrane glycoproteins with respect to the membrane plane was determined by selective iodination with the lactoperoxidase (LPO) technique. Intact RM were labeled on their outer face with 1311 and, after opening of the vesicles with 0.05% DOC, on both faces with 125I. An analysis of iodination ratios for individual proteins separated electrophoretically showed that in most membrane glycoproteins, tyrosine residues are predominantly exposed on the luminal face of the vesicles, which is the same face on which the carbohydrate moieties are exposed. Several membrane glycoproteins are also exposed on the cytoplasmic surface and therefore have a transmembrane disposition. In this study, ribophorins I and II, two integral membrane proteins (mol wt 65,000 and 63,000) characteristic of RM, were found to be transmembrane glycoproteins. It is suggested that the transmembrane disposition of the ribophorins may be related to their possible role in ribosome binding and in the vectorial transfer of nascent polypeptides into the microsomal lumen. KEY WORDS rough microsomes 9The asymmetric distribution of molecular compotransmembrane glycoproteins concanavalin A nents within membranes enables these structures lactoperoxidase iodination 9 ribosome-binding to carry out their function as selective permeability sites barriers between the cell and its environment and 894 J. CELL BIOLOGY 9 The Rockefeller University Press 9 0021-9525/78/0901-089451.00 on

show abstract

“…(31) . The current cytochemical interpretation, however, suggests that in the adult rat liver all the ER membranes are G6Pase positive (33).…”

Section: Methods and Recoveriesmentioning

confidence: 85%

Integrated stereological and biochemical studies on hepatocytic membranes. I.V. Heterogeneous distribution of marker enzymes on endoplasmic reticulum membranes in fractions.

Bolender¹,

Paumgartner²,

Muellener³

et al. 1980

The Journal of Cell Biology

View full text Add to dashboard Cite

The purpose of the study was to consider quantitatively the relationships between the surface area of the endoplasmic reticulum (ER) and constituent marker enzyme activities, as they occur in fractions collected from rat liver homogenates .The ER surface area was estimated in five membrane-containing fractions by use of a combined cytochemical-stereological technique (5), while, at the same time, ER marker enzymes were assayed biochemically . Fraction/homogenate recoveries for the ER enzymes averaged 100%, total membrane surface area 98%, and ER surface area 96% . Relative specific activities, which compare the relative amounts of ER marker enzyme activities to the relative ER surface area in the membranecontaining fractions, indicate variable distributions for glucose-6-phosphatase and NADPH cytochrome c reductase, but not for esterase .The endoplasmic reticulum (ER) of rat liver hepatocytes has been studied extensively by use of marker enzymes to identify the presence of these membranes in fractions (17,14,15,3,1,23,10,11,21) . In recent years, the question as to whether a given amount of marker enzyme activity is associated with a similar amount of ER membrane has become one of increasing importance (15,25,13,44,32,8) . Several papers have suggested that (a) marker enzymes are heterogeneously distributed on the ER and that (b) "ER marker enzymes" may also be attached to membranes other than those of the ER (15,46,2,18,22,29,24,14,41,39,4,38,30) . The existence of such marker enzyme heterogeneities would be expected to have important consequences when one is interpreting bio-J. CELL BIOLOGY © The Rockefeller University Press " 0021-9525/80/06/0577/10 $1 .00 Volume 85 June 1980 577-586 chemical data extrapolated from one fraction to the entire liver, or when one is making corrections for contaminations, particularly if the fractionation procedure leads to a sorting of the heterogeneous ER membranes .In an earlier study (9), the surface areas of the hepatic membranes were determined in each of several fractions collected by differential centrifugation . An average 96% fraction-homogenate recovery for the membrane surface areas, accompanied by an average 95% recovery for several membrane marker enzymes, suggested that, for the most part, both membrane surface area and enzyme activity were being similarly conserved during the fractionation procedure . The study showed the extent to which homogenization forms a pool

show abstract

Differentiation of Endoplasmic Reticulum in Hepatocytes

Cited by 284 publications

References 42 publications

Demonstration of a Metabolically Active Glucose-6-phosphate Pool in the Lumen of Liver Microsomal Vesicles

Demonstration of a Metabolically Active Glucose-6-phosphate Pool in the Lumen of Liver Microsomal Vesicles

Spatial orientation of glycoproteins in membranes of rat liver rough microsomes. II. Transmembrane disposition and characterization of glycoproteins.

Integrated stereological and biochemical studies on hepatocytic membranes. I.V. Heterogeneous distribution of marker enzymes on endoplasmic reticulum membranes in fractions.

Contact Info

Product

Resources

About