摘要:

Summry—The nuclear encoded mitochondrial D‐3‐hydroxybutyrate dehydrogenase (BDH) is synthesized in the cytosal as a larger precursor. This membrane enzyme which requires lecithin for activity plays an essential role in energy metabolism as a ketone bodies‐converting enzyme. A cDNA clone of the rat liver enzyme encompassing an antigenic determinant peptide has been isolated after immunoscreening of a λ gt11 expression library. The nucleotide sequence of this 279‐base cDNA insert contains a single open reading frame of 93 amino‐acids, which represents about a third of the mature enzyme. Amino‐acid sequence analysis predicts a hydrophobic stretch of 29 amino‐acids long which probably functions as membrane anchor domain, or as an important region for the enzyme activation by phospholipid. By using this cDNA probe the BDH gene has been investigated at the mRNA level. There is only one mRNA (2‐kb size) for BDH whatever the studied tissue. The rat gene is differently expressed since its mRNA is already present in the foetus liver while the BDH polypeptide amount is low and its enzymatic activity is not detectable even in the late stage of foetal development. The mRNA content is higher in the liver than in extrahepatic tissues. Adrenalectomy and ovariectomy increase liver mRNA content and polypeptide level, as well as activity of BDH. These effects are totally or partially abolished by corticosterone and estradiol treatments respectively. In addition, a 15‐day hyperlipidic diet stimulates BDH gene expression. Present results show that the gene expression of this mitochondrial enzyme is modulated through development and hormonal and metabolic condit

ISSN:0248-4900    

DOI:10.1016/0248-4900(91)90094-4

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summry—The temperature‐dependence of fluid phase endocytosis was investigated in L929 cells, using a recently described fluorescence approach with trimethylamino‐diphenylhexatriene (TMA‐DPH) [7, 9]. In interaction with cells, this probe is rapidly incorporated into the plasma membrane and follows its intracellular traffic of internalization‐recycling, thus behaving as a suitable marker for fluid phase endocytosis. The kinetics of the process may be followed accurately by simple fluorescence intensity measurements, while complementary fluorescence anistropy and micrographic data may be obtained in parallel with the same probe. It was shown that the formation of endocytic vesicles was not inhibited by cooling the cells, even down to 4°C, but only reduced in a quasi‐linear way with temperature. Conversely the further fusion events between the vesicle and large vacuular bodies (endosomes, lysosomes) were strongly and discontinuously influenced: they were almost totally suppressed below 15°C. The evolution of the membrane fluidity during endocytosis, which was monitored by fluorescence anisotropy measurements, indicated that the fusion inhibition was probably correlated with the inability of the endocytic vesicles to shed their initial clathrin coat at low temperature. Moreover, microscopic observations showed that at low temperature the endocytic vesicles hardly moved from the place of their formation. Pretreatment of the cells with microtubule and microfilament depolymerizing drugs (cytochalasin B, vinblastin) led to the conclusion that the cytoskeleton played little role in the vesicle movements. Altogether, the results suggested that the progression of the vesicles towards the cell core resulted from successive fusion events, which explained why they were considerably showed do

ISSN:0248-4900    

DOI:10.1016/0248-4900(91)90095-5

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summry—The formation of secretion granules has been studied in the Golgi apparatus of granular epithelial cells of frog urinary bladders maintained at room temperature or cooled at 4°C for various lengths of time. In control animals, the Golgi apparatus was composed of the following stacked elements: subjacent to thecis‐rmelement mad up of anastomosed tubules, two elements in themid‐compartment consisted of flattened saccules interconnected by tubules. On thetrans‐face, two or three sacculo‐tubular elements were slightly dilated by an electron dense granular material. In thetrans‐Golgi elements, this material was segregated into dilatations of various sizes and shapes which are continuous with flattened portions devoid of stained material. In thetrans‐Golgi region, free irregular progranules, seemingly formed by rupture of thetrans‐most Golgi elements. In granular cells examined after 4 h at 4°C, all Golgi compartments were affected by the low temperature. Thecis‐half portion of the Golgi apparatus consisted mainly of anastomosed membranous tubules and thecis‐element was no longer recognizable. Thetrans‐compartment was reduced to a few flattened saccules with progranules hardly visible on theirtrans‐aspect. At later time intervals, there was a progressive reconstitution of thecis‐zone while saccular elements started to pile up in thetrans‐compartment. At 24 h, thetrans‐compartment comprised six to eight saccular elements which showed irregular dilatations filled with granular material separated by large flattened portions. These various observations were interpreted as indicating that thetrans‐compartment was a dynamic struct

ISSN:0248-4900    

DOI:10.1016/0248-4900(91)90096-6

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summry—The results of immunoblot analysis performed with a specific monoclonal antibody showed that the intestinal mucosa, pancreas and liver are privileged tissues for the expression of annexin IV. Immunofluorescence labelling of thin frozen sections of these tissues showed a strong concentration of annexin IV along the basolateral domain of the plasma membrane of intestinal absorbing cells, hepatocytes and pancreatic acinar cells, whereas in intestinal mucous secreting cells and centro acinar pancreatic cells, annexin IV was found to be present throughout the cytoplas

ISSN:0248-4900    

DOI:10.1016/0248-4900(91)90097-7

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summry—Nerve fibres form conventional synaptic junctions with gland cells in the corpus cardiacum of the locust,Schistocerca gregaria. They contain synaptic vesicles whose contents are normally electron‐lucent, but which react positively to cytochemical tests for amines (eg, incubation in the false transmitter 5‐OHDA). Secretory granules are also present in the terminals and such inclusions are known to contain neuropeptides. The granules undergo non‐synaptic exocytosis and this process has been visualized by the application of tannic acid. Granule exocytosis gives clear signs of being part of a regulated secretory pathway: it is elevatedin vivoby flight— a natural stimulus known to activate the gland (this effect is blocked by prior injection of trehalose); its incidence is closely correlated with a postsynaptic response, suggesting a role for the materials discharged in short‐term signalling; and when inducedin vitroby high K+, it is Ca2+‐dependent. However, a low level of exocytosis was encountered under all conditions employed, suggesting the existence of a constitutive component. It is postulated that the regulated and constitutive patterns of discharge of neuropeptides are related to the roles of these materials as neurotrans/mittersmodulators and neurotrophic substances,

ISSN:0248-4900    

DOI:10.1016/0248-4900(91)90098-8

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summry—The fundic mucosa of resting and acid‐secreting rabbit stomachs were freeze‐fractured and replicated to compare the intramembranous particles on the parietal cell tubulovesicles (rest) and canaliculus (secretion). The particles were counted and their shadow diameters were measured using an image analysis program. The tubulovesicles bore 9 726 ± 400 particles per μm2(mean ± SD), having a mean diameter of 8.4 nm (n = 2571). The canaliculus bore 8 369 ± 430 particles per μm2, having a mean diameter of 7.7 nm (n = 3259). The data were reproducible: three fractures of tubulovesicles and canaliculus gave essentially the same distributions of particle diameters. By contrast, the frequency distributions of tubulovesicle and of canaliculus particle diameters were significantly different (P<0.0005). Neither the opposite curvatures of tubulovesicle and canaliculus microvillus fractures nor subpopulations populations of tubulovesicles with different particle diameters, were the cause of the difference, since there was only one population of tubulovesicles. We therefore postulate that the diameters of intramembranous particles of tubulovesicles and canaliculus are different and suggest, as a working hypothesis, that the difference could be due to a conformational change of the major intramembranous protein, the (H+,

ISSN:0248-4900    

DOI:10.1016/0248-4900(91)90099-9

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summry—In numerous plant cell walls, the cellulose microfibrils are arranged in a helicoidal pattern which has been considered as an analog to a cholesteric order. Here, we report on the spontaneous helicoidal organization which occurs in acellular conditions from aqueous suspensions of cellulose. The cellulosic mucilage of mature seeds of quince (Cydonia oblongaL) was studied bothin situ(pre‐release mucilage) and after water extraction and inin vitrore‐assembly (prolonged high speed ultracentrifugation, further progressive dehydration and embedding in LR White methacrylate or hydrosoluble melamine resin). The cellulosic component was characterized by the use of cellobiohydrolase (CBH1) bound to colloidal gold, and the glucuronic acid residues of the xylan matrix were characterized by the use of cationised gold. Inside the seeds, the pre‐release mucilage is mostly helicoidal, with the occurrence of more or less ordered domains, which indicate a fluid organization relevant to an actual liquid crystal state. Cytochemical tests revealed the tight association between cellulose and glucuronoxylans, the latter constituting a charged coat around each microfibril. Following the hydration of the seed, a cellulosic suspension was extracted in which microfibrils were totally dispersed. The progressive dehydration of the suspension gave rise to concentrated viscous drops. Ultrastructural observations revealed the occurrence of multidomain organization, from non‐ordered to cholesteric‐like regions, revealing that the mucilage is at the same time crystalline and liquid. This constitutes the first demonstration that liquid crystal type assemblies can arise from crystalline and biological cellulose in aqueous suspension. It strengthens the hypothesis that a transient liquid crystal state must occur during the cellulose ordering. The possible morphogenetic role of the glucuronoxylans in the cholesteric organization of the cellulose i

ISSN:0248-4900    

DOI:10.1016/0248-4900(91)90100-2

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summry—Coelomocytes ofNereis diversicolorsynthesize and secrete vitellogeninin vitro. Using a monoclonal antibody which specifically recognized vitellogenin, we showed by immunocytochemistry that among the coelomocytes only a subpopulation, called eleocytes, countained vitellogenin. These results assert that eleocytes are the vitellogenin producing cells in nereid

ISSN:0248-4900    

DOI:10.1016/0248-4900(91)90101-R

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1991.tb03026.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY