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Results for “Subcellular localization”

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PubMed1997

Nuclear localization of the NS3 protein of hepatitis C virus and factors affecting the localization.

Subcellular localization of the NS2 and NS3 proteins of hepatitis C virus was analyzed. In stable Ltk transfectants inducibly expressing an NS2-NS3 polyprotein (amino acids [aa] 810 to 1463), processed full-size NS2 (aa 810 to 1026) was detected exclusively in a cytoplasmic membrane fraction. On the other hand, the other processed product, carboxy-truncated NS3 (NS3 deltaC1463; aa 1027 to 1463), was present in both cytoplasmic and nuclear fractions. To further analyze subcellular localization of NS3, NS3 deltaC1459 (aa 1027 to 1459), full-size NS3 (NS3F; aa 1027 to 1657), and both amino- and carboxy-truncated NS3 (NS3 deltaNdeltaC; aa 1201 to 1459) were expressed in HeLa cells by using a vaccinia virus-T7 hybrid expression system. NS3 deltaC1459 and NS3F accumulated in the nucleus as well as in the cytoplasm, exhibiting a dot-like staining pattern. On the other hand, NS3 deltaNdeltaC was localized predominantly in the cytoplasm, suggesting the presence of a nuclear localization signal(s) in the amino-terminal sequence of NS3. NS4A, a viral cofactor for the NS3 protease, inhibited nuclear transport of NS3 deltaC1459 and NS3F, with the latter inhibited to a lesser extent than was the former. Interestingly, wild-type p53 tumor suppressor augmented nuclear localization of NS3 deltaC1459 and NS3F, whereas mutant-type p53 inhibited nuclear localization and augmented cytoplasmic localization of NS3 deltaC1459. However, subcellular localization of NS3 deltaNdeltaC was not affected by either type of p53. Wild-type p53-mediated nuclear accumulation of NS3 deltaC1459 and NS3F was inhibited partially, but not completely, by coexpressed NS4A, with NS3F again affected less prominently than was NS3 deltaC1459.

Animals↗

PubMed1994

Subcellular localization of the inositol 1,4,5-trisphosphate receptor, P400, in the vestibular complex and dorsal cochlear nucleus of the rat.

The subcellular localization of the inositol 1,4,5-trisphosphate receptor protein, P400, was studied in the vestibular complex, an area to which Purkinje cells project, as well as in neurons of the dorsal cochlear nucleus and in ectopic Purkinje cells of adult rat brain. The receptor was demonstrated by electron microscopical immunocytochemistry using the avidin-biotin peroxidase complex procedure, with the monoclonal antibody 4C11 raised against mouse cerebellar inositol 1,4,5-trisphosphate receptor protein. Immunoreactivity was found in preterminal fibres and terminal boutons in the nuclei of the vestibular complex, generally associated with the subsurface systems and stacks or fragments of smooth endoplasmic reticulum. Ectopic Purkinje cells and cartwheel cells of the dorsal cochlear nucleus also displayed immunoreactivity, but this was much less intense in the latter. The results of the present study suggest that this receptor protein, involved in the release of Ca2+, is located in sites that enable it to influence the synthesis, transport and release of neurotransmitters.

Animals↗

PubMed2002

Sequence conserved for subcellular localization.

The more proteins diverged in sequence, the more difficult it becomes for bioinformatics to infer similarities of protein function and structure from sequence. The precise thresholds used in automated genome annotations depend on the particular aspect of protein function transferred by homology. Here, we presented the first large-scale analysis of the relation between sequence similarity and identity in subcellular localization. Three results stood out: (1) The subcellular compartment is generally more conserved than what might have been expected given that short sequence motifs like nuclear localization signals can alter the native compartment; (2) the sequence conservation of localization is similar between different compartments; and (3) it is similar to the conservation of structure and enzymatic activity. In particular, we found the transition between the regions of conserved and nonconserved localization to be very sharp, although the thresholds for conservation were less well defined than for structure and enzymatic activity. We found that a simple measure for sequence similarity accounting for pairwise sequence identity and alignment length, the HSSP distance, distinguished accurately between protein pairs of identical and different localizations. In fact, BLAST expectation values outperformed the HSSP distance only for alignments in the subtwilight zone. We succeeded in slightly improving the accuracy of inferring localization through homology by fine tuning the thresholds. Finally, we applied our results to the entire SWISS-PROT database and five entirely sequenced eukaryotes.

Amino Acid Sequence↗

PubMed1981

The subcellular localization of administered N-acetylneuraminic acid in the brains of well-fed and protein restricted rats.

1. This study investigated the subcellular localization of injected N-acetylneuraminic acid (NeuNAc) in brain. Forty pregnant rats were distributed into four groups. Two groups were given a 200 g casein/kg diet and the other two groups a 100 g casein/kg diet throughout gestation. One group from each of the low- and high-protein groups were given their respective diets for the first 11 d of lactation. On day 12 of lactation, 2.5 microCi [14]NeuNAc/kg body-weight were injected intraperitoneally into their pups. After 1 h the pups were killed, their brains removed and subjected to subcellular fractionation. On day 16 of lactation the other two groups were similarly treated. 2. In all groups of animals 80% of the [14C]NeuNAc incorporated into the brains was found in the synaptosomal fraction and the remainder distributed among the other subcellular fractions in proportion to their total NeuNAc content. 3. These results suggest that NeuNAc exerts its effects on behaviour via the synaptic membrane.

Animals↗

PubMed1989

Changes in activity and subcellular localization of alpha-like DNA polymerase during cell cycle of Physarum polycephalum.

Regulation of DNA replication was given attention by examining the subcellular localization of alpha-like DNA polymerase in Physarum polycephalum. The activity per plasmodium increased by 2-fold in the cytoplasm during the G2-phase, and decreased with a concomitant increase in nuclei prior to DNA replication. This would suggest that the enzyme translocates from the cytoplasm to the nucleus, co-ordinately with DNA replication. In nuclei, the nuclear matrix-bound activity increased during the S-phase, but changes did not always parallel the rate of DNA replication. On the other hand, the activity measured without exogenous templates did change with the rate, although the activity was low. It is, therefore, suggested that part of the enzyme binding with the matrix participates in DNA replication.

Binding Sites↗

PubMed1999

The subcellular localization of phospholipase D activities in rat Leydig cells.

Rat Leydig cells contain a phospholipase D (PLD), which can be activated by vasopressin and phorbol ester. In order to clarify which Leydig cell organelles that express PLD activity, the subcellular localization of two differently regulated PLD activities was investigated by subcellular fractionation on a 40% (v/v) self-generating Percoll gradient. PLD activities in broken cells were estimated using radiolabeled didecanoylphosphatidylcholine as a substrate. Initial experiments revealed the presence of an oleate Mg2+ -activated PLD and a phosphatidylinositol 4,5-bisphosphate-activated PLD (PIP2-PLD) in the microsomal fraction of Leydig cells. The latter activity could be further stimulated by recombinant nonmyristoylated ADP ribosylating factor 1 (ARF1) plus GTPgammaS. The peak of oleate Mg2+ -PLD activity colocalized with the plasma membrane marker, whereas the highest specific activity of the PIP2-PLD activity was found in fractions with a slightly lower density than those containing the plasma membrane and trans-Golgi marker enzymes. In order to localize phorbol ester-stimulated PLD activity in intact Leydig cells, the cells were prelabeled with [14C]-palmitate and then stimulated for 15 min with 100 nM 4-beta-phorbol-12-myristate-13-acetate (PMA) in the presence of ethanol or butanol. The PLD product [14C]-phosphatidylethanol, expressed as the percentage of total labeled phospholipids in the fraction, was slightly increased in all Percoll fractions and showed a prominent peak in the fractions containing plasma membrane, trans-Golgi, and fractions of slightly lower density. The PMA-induced formation of [14C]-phosphatidylbutanol could be inhibited dose-dependently with brefeldin A suggesting that the activation of PLD by the phorbol ester was mediated by ARF.

ADP-Ribosylation Factor 1↗

PubMedDate not supplied

Subcellular localization of thyroxine-5-deiodinase in rat liver.

L-Thyroxine (T4) is monodeiodinated to 3,3',5'-triiodothyronine (rT3) and 3,3',5'-triiodothyronine (T3). A recent work has demonstrated that T4-5'-deiodinase is localized solely in the microsomes of rat liver, as was originally suggested. In this study identical subcellular localization was also found for T4-5-deiodinase. This is in contrast with a previous report, indicating that T4-5-deiodinase is present in the soluble cytosol fraction of rat liver. Our results strongly indicate that the thyromimetically active T3 as well as the regulatory active rT3 are both formed from T4 in a microsomal enzyme complex.

Animals↗

PubMed2003

Subcellular localization of human glyceraldehyde-3-phosphate dehydrogenase is independent of its glycolytic function.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was considered a classical glycolytic protein involved exclusively in cytosolic energy production. However, recent evidence suggests that it is a multifunctional protein displaying diverse activities distinct from its conventional metabolic role. These new roles for GAPDH may be dependent on its subcellular localization, oligomeric state or on the proliferative state of the cell. GAPDH is encoded by a single gene without alternate splicing. The regulatory mechanisms are unknown through which an individual GAPDH molecule fulfills its non-glycolytic functions or is targeted to a specific intracellular localization. Accordingly, as a first step to elucidate these subcellular regulatory mechanisms, we examined the interrelationship between the intracellular expression of the GAPDH protein and its glycolytic function in normal human fetal and senior cells. GAPDH localization was determined by immunoblot analysis. Enzyme activity was quantitated by in vitro biochemical assay. We now report that the subcellular expression of GAPDH was independent of its classical glycolytic function. In particular, in both fetal and senior cells, considerable GADPH protein was present in intracellular domains characterized by significantly reduced catalysis. Gradient analysis indicated that this lower activity was not due to the dissociation of tetrameric GAPDH. These results suggest that human cells contain significant intracellular levels of enzymatically inactive GAPDH which is age-independent. The possibility is considered that the functional diversity of GAPDH may be mediated either by posttranslational alteration or by subcellular protein:protein and/or protein:nucleic acid interactions.

Cell Nucleus↗

PubMed1984

Differential subcellular localization of tubulin and the microtubule-associated protein MAP2 in brain tissue as revealed by immunocytochemistry with monoclonal hybridoma antibodies.

The distribution and subcellular localization of tubulin and MAP2 in brain tissue were analyzed by immunocytochemistry with monoclonal hybridoma antibodies prepared against Chinese hamster brain tubulin and MAP2. We examined three anti-tubulin hybridoma antibodies (Tu3B, Tu9B, Tu12) specific for beta-tubulin, and two anti-MAP2 hybridoma antibodies (AP9,AP13). The specificity of each of the monoclonal antibodies was characterized by staining nitrocellulose electrophoretic blots of SDS-polyacrylamide gels of whole brain or hippocampal extracts. Each hybridoma antibody bound only its respective antigen in these preparations. Polyclonal antisera against tubulin were also examined. Sections reacted with antisera against tubulin or monoclonal antibodies against beta-tubulin revealed a wide variety of stained cellular compartments. The reaction product was found to decorate dendritic and axonal microtubles in neurons; glial cells were also stained. MAP2 immunoreactivity was found only in neurons. In the case of one of the monoclonal antibodies (AP9), staining was preferentially associated with dendritic processes. However, light but significant staining of axonal processes was seen with AP13. Within dendrites, MAP2 was found associated with dendritic microtubules and postsynaptic densities (psd), both in shaft and spine synapses. In addition, strong immunoreactivity for MAP2 was found within the cytoplasm of dendritic spines. There was little or no immunoreactivity for tubulin in the spine cytoplasm, although the psd was stained. The localization of MAP2 in dendritic spines and in the psd suggests that this protein may have a biological role independent of its association with microtubules. The observations on differential staining of the hybridoma antibodies against MAP2 suggest that there may be distinct subtypes or states of MAP2 within neurons.

Animals↗

PubMed1999

The subcellular localization of PBX1 and EXD proteins depends on nuclear import and export signals and is modulated by association with PREP1 and HTH.

Nuclear localization of the Extradenticle (EXD) and PBX1 proteins is regionally restricted during Drosophila and mammalian development. We studied the subcellular localization of EXD, PBX, and their partners Homothorax (HTH) and PREP1, in different cell contexts. HTH and PREP1 are cytoplasmic and require association with EXD/PBX for nuclear localization. EXD and PBX1 are nuclear in murine fibroblasts but not in Drosophila Schneider cells, in which they are actively exported to the cytoplasm. Coexpression of EXD/PBX with HTH/PREP1 causes nuclear localization of their heterodimers in both cell contexts. We propose that heterodimerization with HTH/PREP induces nuclear translocation of EXD and PBX1 in specific cell contexts by blocking their nuclear export.

3T3 Cells↗

PubMed1996

Subcellular localization of SV2 and other secretory vesicle components in PC12 cells by an efficient method of preembedding EM immunocytochemistry for cell cultures.

We demonstrated the subcellular localization of SV2, a transmembrane protein associated with neuroendocrine secretory vesicles, in NGF-treated PC12 cells by preembedding EM immunocytochemistry (ICC), using a small gold probe followed by silver enhancement. The use of a multiwell chamber slide substantially improved the efficiency of the preembedding EM ICC procedures for cell cultures. The advantages and related caveats of this method are discussed. SV2 was distinctly localized on dusters of synaptic vesicles and large dense-cored vesicles (LDCV). The distribution of SV2 on these two types of secretory vesicles was compared quantitatively to that of another secretory vesicle-associated transmembrane protein, synaptophysin. In cultures under similar experimental conditions, the ratio of SV2 vs synaptophysin ICC staining on synaptic vesicle dusters was about 1:1, whereas it was about 9:1 on LDCV membranes. Furthermore, whereas SV2 is localized on the membranes of the LDCVs, chromogranin A, an acidic protein in secretory granules, is clearly in the core of the LDCVs. This is the first demonstration of these two antigens in such dose (approximately 20 nm) yet distinct compartments within a single organelle.

Animals↗

PubMed2002

Subcellular localization of basic fibroblast growth factor and fibroblast growth factor receptor 1 in pituitary adenomas.

The aim of this study was to assess the subcellular localization of basic fibroblast growth factor (bFGF) and fibroblast growth factor receptor 1 (FGFR1) in pituitary adenomas. We studied 61 patients who had primary pituitary adenomas and underwent operation. The immunohistochemistry for bFGF, FGFR1, and MIB-1 was examined in paraffin-embedded tissues. The bFGF immunoreactivity in the nucleus was recorded as the bFGF nuclear index, which was calculated as the percentage of tumor cells with the bFGF immunoreactivity in the nuclei when more than 1000 tumor cells were examined. Recurrent adenomas were found in 7 patients during follow-up periods ranging from 8 to 134 months (mean, 57.2). The recurrent adenomas had significantly larger mean bFGF nuclear indices (74.8 +/- 28.8%) than the nonrecurrent adenomas (25.4 +/- 32.1%, P = 0.0003). The bFGF nuclear index also correlated significantly with the maximum tumor diameters and the invasiveness to the cavernous sinuses (Knosp grade) in the adenomas. The cytoplasmic FGFR1 immunoreactivity was inversely correlated (P < 0.02) with maximum tumor diameter. Neither cytoplasmic bFGF, cytoplasmic FGFR1, nor MIB-1 staining index showed any relationship with the recurrence of pituitary adenomas. These findings suggest that the nuclear accumulation of bFGF plays an important role in the progression of pituitary adenomas without its receptors.

Adenoma↗

PubMed1975

Subcellular localization of gamma-aminobutyrate transaminase and glutamate dehydrogenase in adult rat brain. Evidence for at least two small glutamate compartments in brain.

The subcellular localizations of gamma-aminobutyrate transaminase (EC 2.6.1.19) and glutamate dehydrogenase (EC 1.4.1.2) in brain tissue of adult rats were compared with each other and with those of NAD+-isocitrate dehydrogenase (EC 1.1.41) and monoamine oxidase (EC 1.4.3.4; kynuramine as substrate). Crude mitochondrial fractions from brain tissue were centrifuged in continuous sucrose density gradients. gamma-Aminobutyrate transaminase and glutamate dehydrogenase were always found at a higher density than NAD+-isocitrate dehydrogenase and monoamine oxidase. When centrifuged for 1 h at 53 000gav., there was a slight difference between the distribution profiles of glutamate dehydrogenase and gamma-aminobutyrate transaminase. This difference was larger when the centrifugation time was only 15 min. It is concluded that there are subpopulations of brain mitochondria with differing proportions of gamma-aminobutyrate transaminase and glutamate dehydrogenase. The results are discussed in relation to evidence obtained with labelled precursors in vivo that there are at least two small glutamate compartments in adult brain.

4-Aminobutyrate Transaminase↗

PubMed1999

P-glycoprotein subcellular localization and cell morphotype in MDR1 gene-transfected human osteosarcoma cells.

Efflux of chemotherapy agents by P-glycoprotein at the plasma membrane is thought to be a major cause of cancer multidrug-resistance (MDR). However, the mechanism underlying the cellular accumulation and distribution of cytotoxic drugs is still poorly defined. We have recently found that P-glycoprotein is expressed also in the nucleus of MDR cell lines selected in doxorubicin (DXR), suggesting the possible involvement of this protein in the direct extrusion of the drug from the nucleus of resistant cells. In this study, we analyzed the subcellular localization of P-glycoprotein, in a series of U-2 OS osteosarcoma cell clones transfected with MDR1 gene in order to verify whether the nucleus is a constant site for the localization and functional activity of P-glycoprotein, and in which way some aspects of cell morphology related to MDR depend on the subcellular P-glycoprotein localization rather than on the exposure to the selective drug. Our results indicate that to achieve a subcellular drug distribution prevailing in the cytoplasm but not in the nucleus, a significant increase in the expression of P-glycoprotein at the different cellular compartments, including the plasma membrane, the cytoplasm, and the nucleus, is needed, although the in vitro drug resistance appears to be mainly dependent on the expression of P-glycoprotein at the cell surface. With regard to the morphological characteristics of MDR cells involving the cell surface and the chromatin arrangement, the influence of DXR appears to be prevalent, although P-glycoprotein overexpression cannot be excluded.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1997

Subcellular localization and expression pattern of the neurofibromatosis type 2 protein merlin/schwannomin.

To elucidate the physiological function of the neurofibromatosis type 2 (NF2) tumor suppressor protein merlin/schwannomin, we studied the expression pattern and subcellular localization in human fibroblasts by Western blot analyses and immunofluorescence using a polyclonal antibody raised against the C-terminus of merlin. Three of the six merlin isoforms identified in this study (75 kDa, 58 kDa, 45 kDa) have been reported earlier and can be explained by alternative splicing. In addition, we detected higher molecular weight bands of about 110 kDa, 100 kDa and 84 kDa. Although the merlin bands of 100 kDa and 110 kDa may represent homo- or heterodimers, oligomerization due to formation of disulfide bonds was excluded. Furthermore, the isoforms of 84 kDa and 58 kDa were quantitatively extractable in Lubrol WX, indicating a localization in or close to the plasma membrane. The 45 kDa band, however, was not soluble in Lubrol WX compatible with a localization of this NF2 isoform in the endoplasmic reticulum. Applying confocal laser scanning microscopy, merlin was shown to be located in four subcellular compartments: (i) perinuclear in a compartment resembling endoplasmic reticulum, (ii) in ruffling membranes and at the leading edges, (iii) in filopodia, and (iv) at cell/substrate adhesion points. Codistribution of merlin and F-actin filaments was found in filopodia, ruffling membranes and at the insertion points of stress fibers at cell/substrate adhesion junctions as shown by phalloidin-rhodamine staining. Double immunofluorescence analyses of merlin and moesin revealed a colocalization in filopodia and ruffling membranes. The localization of merlin in the actin-rich cortical cytoskeleton corresponds to the ezrin-radixin-moesin family of proteins suggesting the NF2 protein to contribute to the regulation of cell growth by interaction with cytoskeleton-associated proteins.

Base Sequence↗

PubMed1983

Subcellular localization in normal and vitamin A-deficient rat liver of vitamin A serum transport proteins, albumin, ceruloplasmin and class I major histocompatibility antigens.

The subcellular localization in rat liver cells of retinol-binding protein (RBP), prealbumin, ceruloplasmin, albumin, and class I transplantation antigen chains was investigated by radioimmunoassay determinations. The concentration of RBP was high in the rough and smooth endoplasmic reticulum (SER). The relative concentrations of prealbumin, ceruloplasmin and albumin were similar in the endoplasmic reticulum fractions and in the Golgi fraction. Neither of the proteins were found in significant amounts in the post-microsomal supernatant nor in the plasma membrane. The concentrations of the class I transplantation antigen chains were higher in the Golgi fraction than in the endoplasmic reticulum fractions. In the rough endoplasmic reticulum (RER) fraction ceruloplasmin and the class I antigens partially interact with high-molecular weight (MW) components, presumably membrane-bound glycosyltransferases. RBP, prealbumin and albumin seemed to be present in free form within the microsomal lumen. In vitamin A deficiency the RBP and to a lesser extent the prealbumin concentrations in the endoplasmic reticulum fractions were significantly increased, as compared to fractions from normal livers. This suggests that the presence of vitamin A is a prerequisite for the transport of RBP from the endoplasmic reticulum to the Golgi complex. The intracellular concentrations of albumin and ceruloplasmin were not significantly altered by vitamin A deficiency. In contrast, the amounts of the class I antigen heavy chains were found to be increased.

Animals↗

PubMed1984

Subcellular localization of the human neutrophil NADPH oxidase. b-Cytochrome and associated flavoprotein.

Human neutrophils were fractionated by nitrogen cavitation and Percoll density centrifugation, and the subcellular localization of FAD-flavoprotein, b-cytochrome, NADH-cytochrome b5 reductase, and NADPH-dependent cytochrome c reductase were determined in normal cells, cells from two patients with chronic granulomatous disease (CGD), and normal cells that had been stimulated with phorbol myristate acetate. In normal cells, a FAD-flavoprotein is found in a 1:2 molar ratio, with cytochrome b in the fractions containing the specific granules. Triton X-114 phase distribution indicates that the b-cytochrome but not the b-cytochrome-associated flavoprotein is an integral membrane protein. 80% of this flavoprotein, as well as all the b-cytochrome, was absent in these fractions from 2 CGD patients, although these patients had normal quantities of FAD in the fractions containing plasma membranes and cytosol. During stimulation the b-cytochrome-associated flavoprotein of the granules translocates with the b-cytochrome to the plasma membrane where NADPH oxidase is localized. Definition of the role of these NADPH oxidase constituents may provide a molecular description of the normal neutrophil respiratory burst and the molecular defect(s) in CGD.

Cell Fractionation↗

PubMed1995

Subcellular localization and biochemical properties of the enzymes of carbamoyl phosphate and urea synthesis in the batrachoidid fishes Opsanus beta, Opsanus tau and Porichthys notatus

The subcellular localization and biochemical properties of the enzymes of carbamoyl phosphate and urea synthesis were examined in three representatives of fishes of the family Batrachoididae, the gulf toadfish (Opsanus beta), the oyster toadfish (Opsanus tau) and the plainfin midshipman (Porichthys notatus). The primary objective of the study was to compare the biochemical characteristics of these fishes, which represent a range between ammoniotelism and ureotelism (O. beta being facultatively ureotelic), with previous patterns observed for an ammoniotelic teleost (Micropterus salmoides, the largemouth bass) and an obligate ureogenic elasmobranch (Squalus acanthias, the dogfish shark). The present study documents the expression of mitochondrial carbamoyl phosphate synthetase (CPSase) III and cytosolic CPSase II (and its associated enzymes of pyrimidine synthesis, dihydro-orotase and aspartate carbamoyltransferase) in the livers of all three batrachoidid species. Both mitochondrial and cytosolic activities of arginase were present in the livers of all three species, as were cytosolic glutamine synthetase and argininosuccinate synthetase and lyase. However, O. beta also showed mitochondrial glutamine synthetase activity and higher total hepatic levels of glutamine synthetase than either O. tau or P. notatus. Taken together, these observations confirm that the arrangement of these enzymes in the batrachoidid fishes has greater similarity to that of M. salmoides than to that of S. acanthias. However, differences within the family appear to coincide with the different nitrogen excretion strategies. O. tau and P. notatus are primarily ammoniotelic and most closely resemble the ammoniotelic M. salmoides, whereas ureotelism in O. beta is correlated with the presence of a mitochondrial glutamine synthetase and the ability to induce higher total glutamine synthetase activities than O. tau or P. notatus. Additionally, isolated mitochondria from O. beta were able to generate citrulline from glutamine, whereas those from O. tau were not. Also in contrast to S. acanthias, glutamine synthetase activities in the mitochondria of O. beta are consistently lower than those of CPSase III. This and other kinetic observations lend support to the hypothesis that glutamine synthetase may be an important regulatory control point in determining rates of ureogenesis in O. beta.

Journal Article↗