PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “subcellular”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 577 records · Page 32Linked to original sources

Measurement of subcellular metabolite levels in leaves by fractionation of freeze-stopped material in nonaqueous media.

This paper describes a technique for measuring the in vivo metabolite levels in the chloroplast stroma, the cytosol, and the vacuole of spinach (Spinacia oleracea U.S.A. hybrid 424) leaves. Spinach leaves were freeze stopped and the frozen tissue was ground and lyophilized. The dry material was homogenized by sonication in a mixture of carbon tetrachloride and heptane, and fractionated by density gradient centrifugation. Measurements of the activity of marker enzymes in various subcellular compartments show the chloroplastic material mainly appearing in the lightest fractions and the cytosolic material in the middle of the gradient, whereas most of the vacuolar material is found in the heaviest fraction. Using the measured distributions of metabolites and of marker enzymes in each fraction of the gradient, the subcellular distribution of the metabolite can be calculated.As a first application, the new fractionation technique was used to investigate the subcellular contents of malate and sucrose in spinach leaves. The results show striking diurnal changes of sucrose and malate, with both substances primarily located in the vacuolar compartment. About three times more malate is present at the end of the day than at the end of the night. The sucrose content in the vacuole falls from a maximum of 45 millimolars at the end of the day to an almost undetectable value of approximately 1 millimolar at the end of the night.

Journal Article↗

Subcellular Localizations of Two Dolichos biflorus Lectins.

The subcellular localizations of the Dolichos biflorus seed lectin and the structurally related lectin (cross-reactive material [CRM]) from the stems and leaves of this plant were determined by immunofluorescence, immunocytochemistry, and cell fractionation procedures. Subcellular fractionation of the cotyledons using a nonaqueous procedure to minimize disruption of the protein bodies showed that the majority of the seed lectin was associated with the protein body fraction and some lectin was also present in the starch granules. Immunofluorescence and immunocytochemistry at the light microscopic level showed that the seed lectin was mainly localized at the peripheries of these organelles. Lectin was also found in the cytoplasm of the cells, although the amount appeared to be dependent upon the degree of protein body disruption.Immunofluorescence and immunocytochemistry studies of the stem and leaf lectin (CRM) indicated that a significant portion of this lectin may be associated with the cell walls, although lectin was also seen in the cytoplasm of plasmolyzed cells. Extraction and cell fractionation studies showed that a large portion of the CRM is readily solubilized and most of the remainder is pelleted at 1000g. The CRM can be extracted from these pellets by treatment with cellulase and pectinase; other reagents such as NaCl, detergents, and EDTA could also release significant amounts of CRM. These studies suggest that the CRM is noncovalently bound to the cell walls. A comparison of the distribution of exogenously supplied [(125)I]CRM with the endogenous CRM during extraction and cell fractionation indicates that soluble CRM is not adsorbed to the 1000g pellet during fractionation.The different subcellular distributions of these two structurally related lectins suggest that different tissues of the same plant may utilize lectins for different functions.

Journal Article↗

High-throughput viral expression of cDNA-green fluorescent protein fusions reveals novel subcellular addresses and identifies unique proteins that interact with plasmodesmata.

A strategy was developed for the high-throughput localization of unknown expressed proteins in Nicotiana benthamiana. Libraries of random, partial cDNAs fused to the 5' or 3' end of the gene for green fluorescent protein (GFP) were expressed in planta using a vector based on Tobacco mosaic virus. Viral populations were screened en masse on inoculated leaves using a confocal microscope fitted with water-dipping lenses. Each viral infection site expressed a unique cDNA-GFP fusion, allowing several hundred cDNA-GFP fusions to be screened in a single day. More than half of the members of the library carrying cDNA fusions to the 5' end of gfp that expressed fluorescent fusion proteins displayed discrete, noncytosolic, subcellular localizations. Nucleotide sequence determination of recovered cDNA sequences and subsequent sequence searches showed that fusions of GFP to proteins that had a predicted subcellular "address" became localized with high fidelity. In a subsequent screen of >20,000 infection foci, 12 fusion proteins were identified that localized to plasmodesmata, a subcellular structure for which very few protein components have been identified. This virus-based system represents a method for high-throughput functional genomic study of plant cell organelles and allows the identification of unique proteins that associate with specific subcompartments within organelles.

Base Sequence↗

Tissue retention and subcellular distribution of continuously infused melatonin in rats under near physiological conditions.

The fate and disposition of the melatonin released into the circulation is still poorly understood, and almost all current knowledge is derived from measurements made after a single and often a very large dose of labelled melatonin. In continuous infusion experiments in freely moving rats, we have recently demonstrated that considerable amounts of melatonin must be endogenously released in order to achieve and maintain approximately a 10-fold elevation of the low daytime plasma levels of this hormone. We have now applied this infusion paradigm to study the fate and tissue accumulation of [3H]-melatonin continuously infused under near physiological conditions into the jugular vein for a period of 2 hr. The retention of [3H]-melatonin and chloroform-insoluble [3H]-melatonin-metabolites was measured in almost all body tissues and their subcellular compartments immediately at the end of the infusion period and 6 hr later. At the end of the 2 hr infusion period, about 45% of the administered melatonin was recovered as water-soluble metabolites in the urine and about 20% in the small intestine. Some accumulation of [3H]-melatonin-derived water-soluble radioactivity was also noticed in the liver, colon, adrenals, and pituitary, as well as in the feces. The subcellular distribution of this radioactivity differed between tissues. During the period of 6 hr after the termination of infusion, a considerable amount of melatonin-derived radioactivity was found to become increasingly attached to the proteous interlayer of chloroform extracts of tissues and subcellular fractions, from where it could only be liberated by protease treatment.

Adrenal Glands↗

Subcellular localization of hematoporphyrin derivative in bladder tumor cells in culture.

Mitochondria have been implicated as a primary subcellular site of porphyrin localization and photodestruction. However, other organelles including the cell membrane, lysosomes and nucleus have been shown to be damaged by hematoporphyrin derivative (HpD) photosensitized destruction as well. In this study we attempted to follow the translocation of the fluorescent components of HpD in human bladder tumor cells (MGH-U1) in culture to determine whether specific subcellular localization occurs over time. Following a 30 min exposure to HpD the cellular fluorescence was examined immediately and 1, 2, 4, and 24 h after HpD removal using fluorescence microscopy and an interactive laser cytometer. The in vitro translocation of dye appeared to be fairly rapid with fluorescence present at the cell membrane and later (1-2 h) within a perinuclear area of the cytoplasm. To determine whether HpD had become concentrated into a specific subcellular organelle, these fluorescence distribution patterns were compared with fluorescent marker dyes specific for mitochondria, endoplasmic reticulum and other membranous organelles. The HpD fluorescence did not appear to be as discrete as the dyes specific for mitochondria or endoplasmic reticulum but appeared similar to the diffuse cytomembrane stain. Finally, the interaction between the fluorescent components of HpD and the cellular constituents was evaluated using a "fluorescence redistribution after photobleaching" technique. The results indicated that the mean lateral diffusion for HpD in MGH-U1 cells was 1.05 x 10(-8) cm2/s, a rate closer to that of lipid diffusion (10(-8)) than that of protein diffusion (10(-10)).(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Line↗

Cellular and subcellular heterogeneity of [Ca2+]i in single heart cells revealed by fura-2.

Digital imaging of calcium indicator signals (fura-2 fluorescence) from single cardiac cells has revealed different subcellular patterns of cytoplasmic calcium ion concentration ([Ca2+]i) that are associated with different types of cellular appearance and behavior. In any population of enzymatically isolated rat heart cells, there are mechanically quiescent cells in which [Ca2+]i is spatially uniform, constant over time, and relatively low; spontaneously contracting cells, which have an increased [Ca2+]i, but in which the spatial uniformity of [Ca2+]i is interrupted periodically by spontaneous propagating waves of high [Ca2+]i; and cells that are hypercontracted (rounded up) and that have higher levels of [Ca2+]i than the other two types. The observed cellular and subcellular heterogeneity of [Ca2+]i in isolated cells indicates that experiments performed on suspensions of cells should be interpreted with caution. The spontaneous [Ca2+]i fluctuations previously observed without spatial resolution in multicellular preparations may actually be inhomogeneous at the subcellular level.

Animals↗

Identification of mycobacterial surface proteins released into subcellular compartments of infected macrophages.

Considerable effort has focused on the identification of proteins secreted from Mycobacterium spp. that contribute to the development of protective immunity. Little is known, however, about the release of mycobacterial proteins from the bacterial phagosome and the potential role of these molecules in chronically infected macrophages. In the present study, the release of mycobacterial surface proteins from the bacterial phagosome into subcellular compartments of infected macrophages was analyzed. Mycobacterium bovis BCG was surface labeled with fluorescein-tagged succinimidyl ester, an amine-reactive probe. The fluorescein tag was then used as a marker for the release of bacterial proteins in infected macrophages. Fractionation studies revealed bacterial proteins within subcellular compartments distinct from mycobacteria and mycobacterial phagosomes. To identify these proteins, subcellular fractions free of bacteria were probed with mycobacterium-specific antibodies. The fibronectin attachment protein and proteins of the antigen 85-kDa complex were identified among the mycobacterial proteins released from the bacterial phagosome.

Animals↗

Subcellular distribution of marker enzymes in cells of a minute fungus, Fusidium sp. 100-3.

An electron microscope cytochemical technique was used to determine the subcellular distribution of marker enzymes in Fusidium sp. 100-3 cells. Nucleoside diphosphatase was found in the nuclear envelope and intracytoplasmic membrane segment. Thiamine pyrophosphatase was found to be associated with the mesosomes. Cytochrome c (oxidase) activity was found only in the mitochondrial cristae. Strong alkaline phosphatase activity was present in the vacuole; in addition, the enzyme activity was discretely dispersed throughout the cytoplasm without any association with any membrane material. The overall characteristics of the cell ultrastructure and subcellular enzyme distribution of Fusidium sp. 100-3 cells compare fairly well with those of a fungal cell. But there are considerable differences from the characteristics of higher eucaryotic cells. Detailed data on the marker enzymes distribution in a variety of fungal cells are not available. Therefore, it is not possible to conclude whether the marker enzyme distribution of Fusidium sp. 100-3 cells is unique or is typical of any fungal organism. Detailed studies of cell ultrastructure of and marker enzyme distribution in minute fungal cells and their comparison to the ultrastructure of and marker enzyme distribution in other fungal organisms may be helpful in understanding the phylogenetic and ontogenic development of subcellular organelles.

Acid Anhydride Hydrolases↗

Subcellular locations of MOD5 proteins: mapping of sequences sufficient for targeting to mitochondria and demonstration that mitochondrial and nuclear isoforms commingle in the cytosol.

MOD5, a gene responsible for the modification of A37 to isopentenyl A37 of both cytosolic and mitochondrial tRNAs, encodes two isozymes. Initiation of translation at the first AUG of the MOD5 open reading frame generates delta 2-isopentenyl pyrophosphate:tRNA isopentanyl transferase I (IPPT-I), which is located predominantly, but not exclusively, in the mitochondria. Initiation of translation at a second AUG generates IPPT-II, which modifies cytoplasmic tRNA. IPPT-II is unable to target to mitochondria. The N-terminal sequence present in IPPT-I and absent in IPPT-II is therefore necessary for mitochondrial targeting. In these studies, we fused MOD5 sequences encoding N-terminal regions to genes encoding passenger proteins, pseudomature COXIV and dihydrofolate reductase, and studied the ability of these chimeric proteins to be imported into mitochondria both in vivo and in vitro. We found that the sequences necessary for mitochondrial import, amino acids 1 to 11, are not sufficient for efficient mitochondrial targeting and that at least some of the amino acids shared by IPPT-I and IPPT-II comprise part of the mitochondrial targeting information. We used indirect immunofluorescence and cell fractionation to locate the MOD5 isozymes in yeast. IPPT-I was found in two subcellular compartments: mitochondria and the cytosol. We also found that IPPT-II had two subcellular locations: nuclei and the cytosol. The nuclear location of this protein is surprising because the A37-->isopentenyl A37 modification had been predicted to occur in the cytoplasm. MOD5 is one of the first genes reported to encode isozymes found in three subcellular compartments.

Alkyl and Aryl Transferases↗

Two AAA family peroxins, PpPex1p and PpPex6p, interact with each other in an ATP-dependent manner and are associated with different subcellular membranous structures distinct from peroxisomes.

Two peroxins of the AAA family, PpPex1p and PpPex6p, are required for peroxisome biogenesis in the yeast Pichia pastoris. Cells from the corresponding deletion strains (Pp delta pex1 and Pp delta pex6) contain only small vesicular remnants of peroxisomes, the bulk of peroxisomal matrix proteins is mislocalized to the cytosol, and these cells cannot grow in peroxisome-requiring media (J. A. Heyman, E. Monosov, and S. Subramani, J. Cell Biol. 127:1259-1273, 1994; A. P. Spong and S. Subramani, J. Cell Biol. 123:535-548, 1993). We demonstrate that PpPex1p and PpPex6p interact in an ATP-dependent manner. Genetically, the interaction was observed in a suppressor screen with a strain harboring a temperature-sensitive allele of PpPEX1 and in the yeast two-hybrid system. Biochemially, these proteins were coimmunoprecipitated with antibodies raised against either of the proteins, but only in the presence of ATP. The protein complex formed under these conditions was 320 to 400 kDa in size, consistent with the formation of a heterodimeric PpPex1p-PpPex6p complex. Subcellular fractionation revealed PpPex1p and PpPex6p to be predominantly associated with membranous subcellular structures distinct from peroxisomes. Based on their behavior in subcellular fractionation experiments including flotation gradients and on the fact that these structures are also present in a Pp delta pex3 strain in which no morphologically detectable peroxisomal remnants have been observed, we propose that these structures are small vesicles. The identification of vesicle-associated peroxins is novel and implies a role for these vesicles in peroxisome biogenesis. We discuss the possible role of the ATP-dependent interaction between PpPex1p and PpPex6p in regulating peroxisome biogenesis events.

Adenosine Triphosphatases↗

Essential function of the polo box of Cdc5 in subcellular localization and induction of cytokinetic structures.

Members of the polo subfamily of protein kinases play pivotal roles in cell proliferation. In addition to the kinase domain, polo kinases have a strikingly conserved sequence in the noncatalytic C-terminal domain, termed the polo box. Here we show that the budding-yeast polo kinase Cdc5, when fused to green fluorescent protein and expressed under its endogenous promoter, localizes at spindle poles and the mother bud neck. Overexpression of Cdc5 can induce a class of cells with abnormally elongated buds in a polo box- and kinase activity-dependent manner. In addition to localizing at the spindle poles and cytokinetic neck filaments, Cdc5 induces and localizes to additional septin ring structures within the elongated buds. Without impairing kinase activity, conservative mutations in the polo box abolish the ability of Cdc5 to functionally complement the defect associated with a cdc5-1 temperature-sensitive mutation, to localize to the spindle poles and cytokinetic neck filaments, and to induce elongated cells with ectopic septin ring structures. Consistent with the polo box-dependent subcellular localization, the C-terminal domain of Cdc5, but not its polo box mutant, is sufficient for subcellular localization, and its overexpression appears to inhibit cytokinesis. These data provide evidence that the polo box is required to direct Cdc5 to specific subcellular locations and induce or organize cytokinetic structures.

Amino Acid Sequence↗

Distinct subcellular localization patterns contribute to functional specificity of the Cln2 and Cln3 cyclins of Saccharomyces cerevisiae.

The G(1) cyclins of budding yeast drive cell cycle initiation by different mechanisms, but the molecular basis of their specificity is unknown. Here we test the hypothesis that the functional specificity of G(1) cyclins is due to differential subcellular localization. As shown by indirect immunofluorescence and biochemical fractionation, Cln3p localization appears to be primarily nuclear, with the most obvious accumulation of Cln3p to the nuclei of large budded cells. In contrast, Cln2p localizes to the cytoplasm. We were able to shift localization patterns of truncated Cln3p by the addition of nuclear localization and nuclear export signals, and we found that nuclear localization drives a Cln3p-like functional profile, while cytoplasmic localization leads to a partial shift to a Cln2p-like functional profile. Therefore, forcing Cln3p into a Cln2p-like cytoplasmic localization pattern partially alters the functional specificity of Cln3p toward that of Cln2p. These results suggest that there are CLN-dependent cytoplasmic and nuclear events important for cell cycle initiation. This is the first indication of a cytoplasmic function for a cyclin-dependent kinase. The data presented here support the idea that cyclin function is regulated at the level of subcellular localization and that subcellular localization contributes to the functional specificity of Cln2p and Cln3p.

Biological Transport↗

Investigation of tissue organelles by a combination of analytical subcellular fractionation and enzymic microanalysis: a new approach to pathology.

Classical approaches to the study of pathological tissue have relied mainly on morphological techniques. In an attempt to quantitate the abnormalities and to investigate the pathogenesis of tissue disorders at a subcellular level we have combined analytical subcellular fractionation by sucrose density gradient centrifugation with microanalysis of tissue enzymic activities. The methodological problems of performing these studies on milligram quantities of tissue are discussed. Details of the appropriate equipment are provided, and its application to the study of human liver specimens is described. As an example of this approach, biochemical and subcellular fractionation experiments on tissue from patients with both primary and secondary hepatic lysosomal storage diseases are discussed. Examination of the lysosomal changes reveals that increased enzyme activity is a common finding in these disorders but tissue damage occurs only when there is evidence of enhances lysosomal fragility with intracellular release of degradative enzymes. Other tissues which have proved amenable to study in this manner and in which profitable results in the investigation of their disorders have been obtained are listed.

Cell Fractionation↗

Subcellular changes in capillary endothelial cells during repair of hyperoxic lung injury.

We studied the changes in subcellular ultrastructure associated with the hypertrophy of capillary endothelial cells during repair of hyperoxic (100% O2) lung injury in rats. We used stereologic-morphometric measurements at different magnifications to determine the absolute volume of each subcellular compartment per average capillary endothelial cell. The increases in this value during the first 3 days of postexposure repair were 118% for cytoplasm, 786% for polyribosomes, 310% for rough endoplasmic reticulum, and 79% for mitochondria; the volume of pinocytotic vesicles did not change. By day 7 of repair, only the polyribosomes and rough endoplasmic reticulum were still increased; by day 14 all values were normal. We conclude that the capillary endothelial cell hypertrophy that develops during repair of hyperoxic lung injury is associated with large and heterogeneous increases in subcellular organelles and is not merely due to increases in the cytosol or to cellular edema. These increases seem to be an integral part of the repair process and may be important in the development of tolerance to subsequent oxygen exposure.

Animals↗

Control of amyloid-beta-peptide generation by subcellular trafficking of the beta-amyloid precursor protein and beta-secretase.

Amyloid-beta (Abeta) peptides are major components of Alzheimer's disease (AD)-associated senile plaques and generated by sequential cleavage of the beta-amyloid precursor protein (betaAPP) by beta-secretase and gamma-secretase. While beta-secretase activity is exerted by the aspartic protease BACE1, gamma-secretase consists of a protein complex of at least four essential proteins with the presenilins as the catalytically active components. The understanding of the subcellular trafficking of betaAPP and proteases involved in its proteolytic processing has increased rapidly in the last years. BetaAPP as well as the secretases are membrane proteins, and recent work demonstrated that alterations in the lipid composition of cellular membranes could affect the proteolytic processing of betaAPP and Abeta generation. We identified glycosphingolipids as membrane components that modulate the subcellular transport of betaAPP and the generation of Abeta. By cell biological and biochemical methods we also characterized the role of BACE1 and its homologue BACE2 in the proteolytic processing of betaAPP. Here, I summarize and discuss these findings in the context of other studies focused on the function of BACE1 and BACE2 and the role of subcellular trafficking in the proteolytic processing of betaAPP.

Alzheimer Disease↗

Altered subcellular distribution of Na+,K+-ATPase in proximal tubules in young spontaneously hypertensive rats.

During early development of hypertension, the spontaneously hypertensive rat (SHR) demonstrates increased proximal tubule sodium reabsorption. Our previous observations of reduced Na+,K+-ATPase catalytic alpha1 and gamma subunit transcript abundance in SHR proximal tubule led us to test the hypothesis that increased proximal tubule sodium reabsorption may be attributable to altered subunit protein abundance, post-translational modification, or a shift in subcellular alpha1 and gamma distribution toward the basolateral membrane. We now extend previous gene expression studies by analyzing total cellular alpha1 and gamma protein abundance in proximal tubule from SHR compared with matched Wistar-Kyoto (WKY) controls. We also used sucrose density-gradient centrifugation to isolate basolateral, early, and late endosomal membrane-enriched fractions as well as cell surface biotinylation to test the hypothesis of altered subunit subcellular distribution in the SHR proximal tubule. At 4 weeks of age, significantly greater amounts of alpha1 were present in basolateral membrane-enriched fractions of SHR than WKY (21.1+/-1.8% versus 12.3+/-1.8%; P<0.005), and there was a concomitant reduction of alpha1 in late endosomal membrane-enriched fractions of SHR (63.3+/-2.7% versus 74.8+/-4.3%; P<0.05). This finding was confirmed in cell surface biotinylation studies that showed higher alpha1 (1.45+/-0.1-fold greater; P<0.05) and gamma-subunit (3.48+/-0.7-fold greater; P<0.01) abundance in 4-week-old SHR proximal tubule plasma membrane compared with matched WKY samples. These studies support the hypothesis that development of hypertension in SHR may involve an altered subcellular distribution of proximal tubule Na+,K+-ATPase subunits.

Animals↗

Subcellular redistribution of components of the ubiquitin-proteasome pathway during lens differentiation and maturation.

PURPOSE: To determine the subcellular distribution of components of the ubiquitin-proteasome pathway (UPP) in lens epithelium and differentiating fibers and to evaluate potential roles of the UPP in eliminating nuclei and other organelles during maturation of lens fibers. METHODS: Adult bovine lens cryosections were stained for immunofluorescence and analyzed by confocal microscopy. The specificities of the antibodies used in this study were determined by Western blot. results Cryosections of bovine lenses show that E1 and Ubc1 were present in both the cytoplasm and the nucleus in epithelial cells, whereas Ubc3 and ubiquitin conjugates were mostly confined to the nucleus, and Ubc4/5 was preferentially localized in clusters in the vicinity of the nuclear membrane. The 19S and 20S proteasome complexes were preferentially localized in the cytoplasm. When the epithelial cells differentiated into fiber cells at the transition zone, all components of the UPP were primarily present in the nucleus, with the exception of Ubc4/5, which was associated with the nuclear membrane. conclusions The results show that during lens fiber differentiation and maturation, components of the UPP are redistributed at subcellular levels. Subcellular localization of an enzyme indicates where the reaction takes place. The primary nuclear localization of the UPP components in the differentiating fibers supports the hypothesis that the UPP may play a role in elimination of nuclei and other organelles during differentiation and maturation of lens fibers.

Animals↗

Identification and subcellular localization of human rab5b, a new member of the ras-related superfamily of GTPases.

Members of the mammalian rab family of GTPases are associated with specific subcellular compartments, where these proteins are postulated to function in vesicular transport. By screening a human umbilical vein endothelial cell library with degenerate oligonucleotide probes, we have isolated a 1.6-kb cDNA clone encoding a 215-amino-acid protein belonging to the rab family of GTPases. This newly identified rab protein is 81% identical to human rab5, the canine counterpart of which has been localized to the plasma membrane and early endosomes. In light of this homology, we have named this new member of the GTPase superfamily "rab5b." Northern analysis using the rab5b cDNA as a probe revealed a 3.6-kb mRNA in a variety of cell types, including human umbilical vein endothelial cells, K562 erythroleukemia cells, U937 monoblastic cells, and HeLa cells. A fusion protein between glutathione-S-transferase (GST) and rab5b was expressed in bacteria and purified to homogeneity. The recombinant protein was shown to bind GTP and GDP. As is typical of other recombinant rab proteins, the rab5b-GST fusion protein displayed a low intrinsic rate of GTP hydrolysis (0.005/min). An antiserum to rab5b was prepared and used to determine the apparent molecular size and subcellular distribution of the protein. Western blotting with this antibody revealed a 25-kD protein in COS cells transfected with rab5b and in nontransfected HeLa cells. Indirect immunofluorescence and subcellular fractionation showed that rab5b localizes to the plasma membrane. We speculate that rab5b plays a role in vesicular trafficking at the plasma membrane in various cell types.

Amino Acid Sequence↗