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PubMed1988

Subcellular localization of a thromboxane A2/prostaglandin H2 receptor antagonist binding site in human platelets.

The subcellular localization of a binding site for the competitive thromboxane A2/prostaglandin H2 (TXA2/PGH2) antagonist, 9,11-dimethylmethano-11,12-methano-16-(3-iodo-4- hydroxyphenyl)-13,14-dihydro-13-aza-15 alpha beta-omega-tetranor TXA2 ([125I]-PTA-OH), was determined. Subcellular fractions of platelets were prepared by glycerol lysis or nitrogen cavitation, and were characterized by the use of enzymatic markers specific for plasma membranes, endoplasmic reticulum (dense tubular system), mitochondria, granules, and cytosolic constituents. The Kd and density of binding sites in the subcellular fractions were determined by Scatchard analysis of equilibrium binding data. The Kd and Bmax for [125I]-PTA-OH determined in the lysates were 49 +/- 11 nM and 4.1 +/- 1.7 pmol/mg protein respectively (N = 6). The Kd values were not significantly different in any of the fractions assayed. The binding sites were coenriched (4.5 +/- 0.66 fold) with the enzymatic markers for plasma membranes (3.7 +/- 0.5 fold) and dense tubular system (2.4 +/- 0.4 fold). The binding sites were not coenriched with markers for cytoplasmic constituents, mitochondria, or granules. The ability of the TXA2/PGH2 mimetic U46619 to compete with [125I]-PTA-OH for the binding site was also determined for the various subcellular fractions. The IC50 for U46619 was 5.4 +/- 1.2 microM in the lysate, and was not significantly different in the subcellular fractions. These data suggest that the binding site is the TXA2/PGH2 receptor described previously. These data are consistent with the notion that the putative TXA2/PGH2 receptor is localized in the plasma membranes and/or the dense tubular system.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

PubMed1992

Prostaglandin profile and synthetic capacity of the colon: comparison of tissue sources and subcellular fractions.

Although there has been intense interest in the physiology and pathophysiology of prostaglandins (PGs) synthesized in the colon, little is known about the PG profile and synthetic capacity of different tissue sources and subcellular fractions as enzyme sources. Subcellular fractions prepared from the mucosa and muscle layer of rat colon were incubated with or without exogenous arachidonic acid ([3H]20:4n-6) for 30 min. In experiments with exogenous [3H]20:4n-6, the prostaglandin synthetic capacity of the colonic muscle layer was significantly higher than that of the mucosa. Among the subcellular fractions, microsomes had the highest PG synthetic capacity in both mucosa and muscle. The major PG product was PGI2 and PGD2 in the mucosal microsomes and PGI2 and PGE2 in the muscularis microsomes. However, production of PGI2 in the mucosa and PGE2 in the muscle was significantly reduced in the fractions containing both cytosol and microsome, resulting in an alteration of the PG profile. Substrate availability (exogenous vs endogenous supply) appears to influence the PG profile of the colon. In the colonic mucosa with exogenous [3H]20:4n-6, the production of PGI2 was 5 times higher than that of PGE2, whereas the production of PGE2 was twice higher than that of PGI2 in experiments with endogenous 20:4n-6. These observations indicate: 1) different PG profile and synthetic capacity of tissue sources and subcellular fractions; 2) alteration of PG profile due to the variation of 20:4n-6 availability. Thus, the outcome of experiments on the physiological role of PG in the colon may be determined, in part, by the tissue source and subcellular fraction selected for analysis. The present study also suggests that the variation of substrate availability in physiological and pathophysiological processes may affect the PG profile of the colon.

4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyraz↗

PubMed2005

Using Nearest Feature Line and Tunable Nearest Neighbor methods for prediction of protein subcellular locations.

The subcellular location of a protein is closely correlated with it biological function. In this paper, two new pattern classification methods termed as Nearest Feature Line (NFL) and Tunable Nearest Neighbor (TNN) have been introduced to predict the subcellular location of proteins based on their amino acid composition alone. The simulation experiments were performed with the jackknife test on a previously constructed data set, which consists of 2,427 eukaryotic and 997 prokaryotic proteins. All protein sequences in the data set fall into four eukaryotic subcellular locations and three prokaryotic subcellular locations. The NFL classifier reached the total prediction accuracies of 82.5% for the eukaryotic proteins and 91.0% for the prokaryotic proteins. The TNN classifier reached the total prediction accuracies of 83.6 and 92.2%, respectively. It is clear that high prediction accuracies have been achieved. Compared with Support Vector Machine (SVM) and Nearest Neighbor methods, these two methods display similar or even higher prediction accuracies. Hence, we conclude that NFL and TNN can be used as complementary methods for prediction of protein subcellular locations.

Algorithms↗

PubMed2006

Subcellular translocation signals regulate Geminin activity during embryonic development.

BACKGROUND INFORMATION: Geminin (Gem) is a protein with roles in regulating both the fidelity of DNA replication and cell fate during embryonic development. The distribution of Gem is predominantly nuclear in cells undergoing the cell cycle. Previous studies have demonstrated that Gem performs multiple activities in the nucleus and that regulation of Gem activation requires nuclear import in at least one context. In the present study, we defined structural and mechanistic features underlying subcellular localization of Gem and tested whether regulation of the subcellular localization of Gem has an impact on its activity in cell fate specification during embryonic development. RESULTS: We determined that nuclear localization of Gem is dependent on a bipartite NLS (nuclear localization signal) in the N-terminus of Xenopus Gem protein. This bipartite motif mapped to a Gem N-terminal region previously shown to regulate neural cell fate acquisition. Microinjection into Xenopus embryos demonstrated that import-deficient Gem was incapable of modulating ectodermal cell fate, but that this activity was rescued by fusion to a heterologous NLS. Cross-species comparison of Gem protein sequences revealed that the Xenopus bipartite signal is conserved in many non-mammalian vertebrates, but not in mammalian species assessed. Instead, we found that human Gem employs an alternative N-terminal motif to regulate the protein's nuclear localization. Finally, we found that additional mechanisms contributed to regulating the subcellular localization of Gem. These included a link to Crm1-dependent nuclear export and the observation that Cdt1, a protein in the pre-replication complex, could also mediate nuclear import of Gem. CONCLUSIONS: We have defined new structural and regulatory features of Gem, and showed that the activity of Gem in regulating cell fate, in addition to its cell-cycle-regulatory activity, requires control of its subcellular localization. Our data suggest that rather than being constitutively nuclear, Gem may undergo nucleocytoplasmic shuttling through several mechanisms involving distinct protein motifs. The use of multiple mechanisms for modulating Gem subcellular localization is congruent with observations that Gem levels and activity must be stringently controlled during cell-cycle progression and embryonic development.

Active Transport, Cell Nucleus↗

PubMed2003

The molecular basis of differential subcellular localization of C2 domains of protein kinase C-alpha and group IVa cytosolic phospholipase A2.

The C2 domain is a Ca(2+)-dependent membrane-targeting module found in many cellular proteins involved in signal transduction or membrane trafficking. C2 domains are unique among membrane targeting domains in that they show a wide range of lipid selectivity for the major components of cell membranes, including phosphatidylserine and phosphatidylcholine. To understand how C2 domains show diverse lipid selectivity and how this functional diversity affects their subcellular targeting behaviors, we measured the binding of the C2 domains of group IVa cytosolic phospholipase A(2) (cPLA(2)) and protein kinase C-alpha (PKC-alpha) to vesicles that model cell membranes they are targeted to, and we monitored their subcellular targeting in living cells. The surface plasmon resonance analysis indicates that the PKC-alpha C2 domain strongly prefers the cytoplasmic plasma membrane mimic to the nuclear membrane mimic due to high phosphatidylserine content in the former and that Asn(189) plays a key role in this specificity. In contrast, the cPLA(2) C2 domain has specificity for the nuclear membrane mimic over the cytoplasmic plasma membrane mimic due to high phosphatidylcholine content in the former and aromatic and hydrophobic residues in the calcium binding loops of the cPLA(2) C2 domain are important for its lipid specificity. The subcellular localization of enhanced green fluorescent protein-tagged C2 domains and mutants transfected into HEK293 cells showed that the subcellular localization of the C2 domains is consistent with their lipid specificity and could be tailored by altering their in vitro lipid specificity. The relative cell membrane translocation rate of selected C2 domains was also consistent with their relative affinity for model membranes. Together, these results suggest that biophysical principles that govern the in vitro membrane binding of C2 domains can account for most of their subcellular targeting properties.

Calcium↗

PubMed1968

The subcellular distribution of antigen in macrophages.

The intracellular fate of phagocytosed antigens in cells from peritoneal exudate in CBA mice has been studied by using (126)I and (131)I labeled antigens. After uptake of labeled antigen, cells were homogenized and the subcellular fractions were analyzed by isopycnic centrifugation in a sucrose gradient. The uptake of heat-denatured BSA (c BSA) by these cells in vivo is 3.5 microg/mg c BSA injected/10(8) cells. The uptake by cells in animals which were exposed 2 days earlier to 900 r whole body irradiation is slightly lower but does not differ significantly. 90% of the phagocytosed material is degraded within 2-3 hr, the residual 10% is retained at least over an 8 hr periods. Using a pulse and chase technique, with (125)I and (131)I c BSA in vitro and in vivo it was shown that newly phagocytosed antigen is found mainly in a lysosomal turnover compartment of a density 1.19 g cm(-3). Antigen which has been in the cells for longer was found in a denser fraction (1.26 g cm(-3)). In a comparison of nhrmal and X-irradiated cells it can be shown that after irradiation with 900 r less c BSA is found in this storage compartment. Binding of the antigen to the subcellular fractions, and its behavior towards several detergents has been studied. Subcellular fractions do not have the increased immunogenic capacity of antigen enclosed in living macrophages. Two synthetic polypeptide antigens, poly(D-Tyr, D-Glu, D-Ala) and poly-(L-Tyr, L-Glu) have a different subcellular distribution from c BSA, BSA, or bovine gamma globulin. Apart from also being found in the 1.26 storage compartment the polypeptide antigens are mainly located in a 1.15 compartment and only to a small extent in the 1.19 compartment. The half-life of these antigens in the cells is much longer than the half-life of the protein antigens studied. The finding of several subcellular compartments is discussed in connection with the functions possibly performed by macrophages.

Acid Phosphatase↗

PubMed2006

SUBA: the Arabidopsis Subcellular Database.

Knowledge of protein localisation contributes towards our understanding of protein function and of biological inter-relationships. A variety of experimental methods are currently being used to produce localisation data that need to be made accessible in an integrated manner. Chimeric fluorescent fusion proteins have been used to define subcellular localisations with at least 1100 related experiments completed in Arabidopsis. More recently, many studies have employed mass spectrometry to undertake proteomic surveys of subcellular components in Arabidopsis yielding localisation information for approximately 2600 proteins. Further protein localisation information may be obtained from other literature references to analysis of locations (AmiGO: approximately 900 proteins), location information from Swiss-Prot annotations (approximately 2000 proteins); and location inferred from gene descriptions (approximately 2700 proteins). Additionally, an increasing volume of available software provides location prediction information for proteins based on amino acid sequence. We have undertaken to bring these various data sources together to build SUBA, a SUBcellular location database for Arabidopsis proteins. The localisation data in SUBA encompasses 10 distinct subcellular locations, >6743 non-redundant proteins and represents the proteins encoded in the transcripts responsible for 51% of Arabidopsis expressed sequence tags. The SUBA database provides a powerful means by which to assess protein subcellular localisation in Arabidopsis (http://www.suba.bcs.uwa.edu.au).

Arabidopsis Proteins↗

PubMed1999

Protein subcellular location prediction.

The function of a protein is closely correlated with its subcellular location. With the rapid increase in new protein sequences entering into data banks, we are confronted with a challenge: is it possible to utilize a bioinformatic approach to help expedite the determination of protein subcellular locations? To explore this problem, proteins were classified, according to their subcellular locations, into the following 12 groups: (1) chloroplast, (2) cytoplasm, (3) cytoskeleton, (4) endoplasmic reticulum, (5) extracell, (6) Golgi apparatus, (7) lysosome, (8) mitochondria, (9) nucleus, (10) peroxisome, (11) plasma membrane and (12) vacuole. Based on the classification scheme that has covered almost all the organelles and subcellular compartments in an animal or plant cell, a covariant discriminant algorithm was proposed to predict the subcellular location of a query protein according to its amino acid composition. Results obtained through self-consistency, jackknife and independent dataset tests indicated that the rates of correct prediction by the current algorithm are significantly higher than those by the existing methods. It is anticipated that the classification scheme and concept and also the prediction algorithm can expedite the functionality determination of new proteins, which can also be of use in the prioritization of genes and proteins identified by genomic efforts as potential molecular targets for drug design.

Algorithms↗

PubMed1978

Subcellular metabolite concentrations. Dependence of mitochondrial and cytosolic ATP systems on the metabolic state of perfused rat liver.

Mitochondrial and cytosolic contents of adenine nucleotides and phosphate were measured in perfused rat livers employing a technique of fractionation of freeze-fixated tissue in non-aqueous solvents. From the subcellular contents the mitochondrial and cytosolic concentrations of ATP, ADP, AMP and phosphate and the phosphorylation potentials of the subcellular ATP systems were calculated. An attempt was made to elucidate the relationship between mitochondrial and cytosolic adenine nucleotide systems and the dependency on the metabolic state of the liver. The following results were obtained: 1. Under all metabolic conditions studied the mitochondrial ATP/ADP ratios were considerably lower than the cytosolic ratios (mitochondria: 0.1-0.7; cytosol: 2-11). 2. The ATP/ADP ratios calculated from overall tissue contents reflect mainly the cytosolic ratios. 3. An inverse relationship was found between mitochondrial and cytosolic ATP/ADP ratios, i.e. when the mitochondrial ratios tended to increase, the cytosolic ratios decreased and vice versa. 4. The phosphorylation potentials calculated from the subcellular concentrations were higher in the cytosol than in the mitochondria. The potential difference varied between 11 and 3 kj/mol in livers from fed and starved rats, respectively. 5. In the presence of mitochondrial inhibitors, i.e. amytal, dinitrophenol and carboxyatractyloside, the potential difference between the subcellular ATP systems decreased predominantly due to an increase in the mitochondrial ATP/ADP ratios. 6. A correlation between mitochondrial ATP/ADP ratios and the respiratory rates was not observed, but the subcellular ratios appeared to correlate with the rate of glycolysis. When the rate of lactate + pyruvate production was increased, the cytosolic ATP/ADP ratios were increased, too, whereas the mitochondrial ratios tended to decrease. 7. The adenine nucleotides in the cytosol appear to be in near equilibrium catalysed by the adenylate kinase. In the mitochondria, the AMP concentration is much lower than to be expected under equilibrium conditions. These results were discussed with respect to rate control of processes involved in ATP generation, i.e. oxidative phosphorylation, adenine nucleotide translocation and glycolysis.

Adenosine Diphosphate↗

PubMed2007

Subcellular location of serum- and glucocorticoid-induced kinase-1 in renal and mammary epithelial cells.

Serum- and glucocorticoid-induced kinase-1 (SGK1) is involved in aldosterone-induced Na(+) reabsorption by increasing epithelial Na(+) channel (ENaC) activity in cortical collecting duct (CCD) cells, but its exact mechanisms of action are unknown. Although several potential targets such as Nedd4-2 have been described in expression systems, endogenous substrates mediating SGK1's physiological effects remain to be identified. In addition, subcellular localization studies of SGK1 have provided controversial results. We determined the subcellular location of SGK1 using SGK1-autofluorescent protein (AFP) fusion proteins. Rabbit CCD (RCCT-28A) cells were transiently transfected with a construct encoding for SGK1-AFP and were stained or cotransfected with markers for various subcellular compartments. In live cells, transiently expressed SGK1-AFP clearly colocalized with the mitochondrial marker rhodamine 123. Similarly, SGK1-AFP colocalized with the mitochondrial marker MitoTracker when stably expressed using a retroviral system in either RCCT-28A cells or the mammary epithelial cell line MCF10A. To determine which region of SGK1 is responsible for this subcellular localization, we generated RCCT-28A cell lines stably expressing SGK1 mutants. The results indicate that the NH(2)-terminal 60-amino acid region of SGK1 is necessary and sufficient for its subcellular localization. Localization of SGK1 to the mitochondria raises the possibility that SGK1 may play a role in regulating energy metabolism.

Animals↗

PubMed1996

Natural anthracenone subcellular distribution and effects on NADPH-cytochrome P450 reductase microsomal activity.

Natural anthracenone subcellular distribution and effects on NADPH-cytochrome P450 reductase microsomal activity. Subcellular distribution study of a natural anthracenone (T-514) isolated from Karwinskia humboldtiana showed to be homogeneous on subcellular (nuclear, mitochondrial, peroxisomal and microsomal) fractions prepared from rat liver treated with an acute dose of T-514. These results indicate that T-514 can pass easily through subcellular compartment membranes and an absence of selectivity for some subcellular organelles. A significant increase of protein on liver homogenates and NADPH-cytochrome P450 reductase microsomal activity indicates that T-514 may act as a microsomal enzymatic inducer. In addition, this enzymatic specific activity increment could be due to the interaction of T-514 with the microsomal redox cycling.

Animals↗

PubMed1999

Relationship between inositol 1,4,5-trisphosphate receptor isoforms and subcellular Ca2+ signaling patterns in nonpigmented ciliary epithelia.

PURPOSE: Subcellular Ca2+ signaling patterns, such as Ca2+ waves, gradients, and oscillations, are an important aspect of cell regulation, but the molecular basis for these signaling patterns is not understood. Because Ca2+ release patterns differ among isoforms of the inositol 1,4,5-trisphosphate (InsP3) receptor, the relationship between the distribution of these isoforms and subcellular Ca2+ signaling patterns in nonpigmented epithelial (NPE) cells was investigated. METHODS: The distributions of the types I, II, and III InsP3 receptors were determined in NPE cells by immunofluorescence, and subcellular Ca2+ signaling patterns in these cells were examined by confocal line scanning microscopy. RESULTS: The type I InsP3 receptor was concentrated at the basal pole of NPE cells, whereas the type III receptor was localized to the apical pole. The type II InsP3 receptor was not expressed in detectable amounts. Acetylcholine induced increases in Ca2+ that were mediated by InsP3, and these Ca2+ increases began as Ca2+ waves that were initiated at the apical pole, in the region of the type III InsP3 receptor. Acetylcholine occasionally induced sustained or repetitive Ca2+ increases that were prominent at the basal pole, in the region of the type I InsP3 receptor, but only subtle or absent apically. CONCLUSIONS: Because the type I InsP3 receptor is thought to be responsible for repetitive Ca2+ release events, and the type III InsP3 receptor instead is suited to initiate Ca2+ signals, the subcellular distribution of these two isoforms corresponds to the Ca2+ signaling patterns observed in this cell type. Differential subcellular expression of InsP3 receptor isoforms may be an important molecular mechanism by which NPE cells organize their Ca2+ signals in space and time.

Acetylcholine↗

PubMed1993

Platelet multielemental composition, lability, and subcellular localization.

Diagnostic X-ray spectrometry (DXS), based on X-ray fluorescence, was used to quantitate directly the multiple elemental composition of washed, intact human platelets (n = 16), with the following results: K = 3.08 +/- 1.00 mg/g, Ca = 1.18 +/- 0.29 mg/g, Zn = 35 +/- 9 micrograms/g. These values show that washed platelets contain significant pools of K, Ca, and Zn, the latter some 30-60-fold higher than plasma levels. Dialysis of whole platelets against cation exchange resin (Chelex-100) did not extract Ca(II) and Zn(II) sequestered within whole cells. To identify the subcellular locale of the elements, platelet lysate was subjected to 30-70% sucrose gradient ultracentrifugation and subcellular enriched fractions were obtained. Fractions were analyzed by DXS (for elements), electron microscopy (for dense granules), and subcellular markers fibrinogen and von Willebrand factor. In contrast to Ca and K, which accumulate in the dense granules and the cytoplasm, respectively, Zn appears to be distributed in the alpha-granules (40%) and the cytoplasm (60%). The subcellular distribution of Zn(II) is discussed within the context of the sensitivity of platelet response to the availability of Zn(II) and the platelet release reactions following stimulation.

Absorption↗

PubMed2006

Characterisation of organellar proteomes: a guide to subcellular proteomic fractionation and analysis.

Subcellular fractionation is being widely used to increase our understanding of the proteome. Fractionation is often coupled with 2-DE, thus allowing the visualisation of proteins and their subsequent identification and characterisation by MS. Whilst this strategy should be effective, to date, there has been little or no consideration given to differences in the mass, pI, hydropathy or abundance of proteins in the organelles and how analytical strategies can be tailored to match the idiosyncrasies of proteins in each particular compartment. To address this, we analysed 3962 Saccharomyces cerevisiae proteins, previously localised to one or more of 22 subcellular compartments. Different compartments showed significantly different distributions of protein pI and hydropathy. Mitochondrial and ER proteins showed the most dramatic differences to other organelles, in their protein pIs and hydropathy, respectively. We show that organelles can be clustered by similarities in these physicochemical protein characteristics. Interestingly, the distribution of protein abundance was also significantly different between many organelles. Our results show that to fully explore subcellular fractions of the proteome, specific analytical strategies should be employed. We outline strategies for all 22 subcellular compartments.

Cell Compartmentation↗

PubMed2006

Alteration of protein subcellular location and domain formation by alternative translational initiation.

Alternative translation is an important cellular mechanism contributing to the generation of proteins and the diversity of protein functions. Instead of studying individual cases, we systematically analyzed the alteration of protein subcellular location and domain formation by alternative translational initiation in eukaryotes. The results revealed that 85.7% of alternative translation events generated biological diversity, attributed to different subcellular localizations and distinct domain contents in alternative isoforms. Analysis of isoelectric point values revealed that most N-terminal truncated isoforms significantly lowered their isoelectric point values targeted at different subcellular localizations, whereas they had conserved domain contents the same as the full-length isoforms. Furthermore, Fisher's exact test indicated that the two ways-targeting at different cellular compartments and changing domain contents-were negatively associated. The N-term truncated isoforms should have only one way to diversify their functions distinct from the full-length ones. The peculiar consequence of subcellular relocation as well as change of domain contents reflected the very high level of biological complexity as alternative usage of initiation codons.

Animals↗

PubMed1996

The subcellular distribution of eukaryotic translation initiation factor, eIF-5A, in cultured cells.

To gain insight into the role of the eukaryotic translation initiation factor, eIF-5A, we investigated the subcellular distribution of this protein in several cultured cell types and at different stages of the cell cycle using a highly potent monospecific polyclonal antibody to eIF-5A. Studies using indirect immunofluorescence and confocal microscopy in conjunction with subcellular fractionation demonstrate that eIF-5A is primarily localized in the cytoplasm of cells. This cytoplasmic location of eIF-5A is not significantly altered in different stages of the cell cycle and the subcellular distribution pattern of eIF-5A is not changed by viral oncogene transformation. Cell fractionation experiments identified two populations of eIF-5A in the cytoplasm, a soluble fraction and a fraction bound to internal membranes. By double immunofluorescence staining with an antibody against calnexin, a resident protein of the endoplasmic reticulum (ER), we demonstrate that the membrane-bound fraction of eIF-5A colocalizes with the ER and not with the cytoskeleton. Expression of Rev, a regulatory protein of human immunodeficiency virus type 1 (HIV-1), does not alter the subcellular distribution of endogenous eIF-5A in these cells. eIF-5A is detected in all tissues and cells examined including extracts prepared from Xenopus oocytes. Our results indicate that eIF-5A is a ubiquitous cytoplasmic protein and suggest that a site of eIF-5A function is likely to be in association with the ER.

3T3 Cells↗

PubMed1999

Subcellular distribution of free fatty acids, phospholipids, and endogenous lipase activity of rabbit urinary bladder smooth muscle and mucosa.

OBJECTIVES: The urinary bladder wall can be separated into two major compartments: the urothelium (mucosa) and the detrusor smooth muscle. Specific dysfunctions of both layers have been linked to ischemia, which may induce significant cellular and subcellular membrane damage via the activation of selective calcium dependent and independent hydrolytic enzymes. Preliminary to investigating changes in cell membrane composition induced by ischemia, we measured the free fatty acid (FFA) and phospholipid (PL) content of normal rabbit bladder muscle and mucosal cellular and subcellular membranes, and characterized the endogenous lipase activity. METHODS: Rabbit bladders were excised and the muscle and mucosal layers separated; each layer was homogenized, then fractionated by differential centrifugation. Endogenous lipase activity of the homogenates, and FFA and PL concentrations of the homogenates and subcellular fractions were measured. RESULTS: (1) The basal FFA concentration of the mucosal homogenates was 5 times that of the muscle homogenates. (2) The basal PL concentrations of the two tissues were similar. (3) Subcellular studies: FFA concentration was greatest in the mitochondrial fraction of both compartments. In the mucosa, PL concentration was significantly greater in the mitochondria and microsomes than in the other fractions; in the smooth muscle, the PL concentration was highest in the mitochondria. (4) The maximal endogenous lipase activity was 10 times higher in the mucosal homogenates than in the muscle homogenates. CONCLUSIONS: These results are consistent with those of previous studies which indicate that the mucosa is metabolically more active than the resting smooth muscle, which may cause the mucosa to be significantly more sensitive than the muscle to hypoxic/ischemic damage.

Animals↗

PubMed1980

The subcellular biochemistry of thyroid.

In this review the subcellular localization of enzymes and constituents in thyroid is discussed. Conditions and results of differential pelleting and gradient centrifugation studies are described with special attention to the validity of the markets used (Table VI). Special approaches to the isolation and characterization of thyroid organelles and membranes are extensively reviewed (Table VII). Subcellular fractionation of thyroid tissue has been shown to be an arduous task. Classic approaches for differential pelleting and gradient centrifugation, which have been proved successful for rat liver, are not always equally satisfactory for thyroid. The major problem is the toughness of the tissue requiring rather traumatizing homogenizing procedures. Nevertheless, the fractionation procedures did allow the subcellular localization of some enzymes and constituents to be established with a high degree of certainty. Furthermore, enriched subcellular fractions have been isolated which have been useful for biochemical studies concerning the specific function of this tissue.

Animals↗