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941.
D. Chrétien Henrik Flyvbjerg Stephen D. Fuller 《European biophysics journal : EBJ》1998,27(5):490-500
The superposition of the regular arrangement of tubulin subunits in microtubules gives rise to moiré patterns in cryo-electron micrographs. The moiré period can be predicted from the dimensions of the tubulin subunits and their arrangement in the surface lattice. Although the average experimental moiré period is usually in good agreement with the theoretical one, there is variation both within and between microtubules. In this study, we addressed the origin of this variability. We examined different possibilities, including artefacts induced by the preparation of the vitrified samples, and variations of the parameters that describe the microtubule surface lattice. We show that neither flattening nor bending of the microtubules, nor changes in the subunit dimensions, can account for the moiré period variations observed in 12 and 14 protofilament microtubules. These can be interpreted as slight variations, in the range –0.5 Å to +0.9 Å, of the lateral interactions between tubulin subunits in adjacent protofilaments. These results indicate that the inter-protofilament bonds are precisely maintained in microtubules assembled in vitro from pure tubulin. The fact that the moiré period is not affected by bending indicates that the local interactions between tubulin subunits are sufficiently stiff to accommodate large deformations of the microtubule wall. 相似文献
942.
Liver metabolism in cold hypoxia: a comparison of energy metabolism and glycolysis in cold-sensitive and cold-resistant mammals 总被引:2,自引:0,他引:2
T. A. Churchill K. M. Cheetham S. Simpkin C. J. Green L. C. H. Wang B. J. Fuller 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1994,164(5):396-404
The effects of cold hypoxia were examined during a time-course at 2 °C on levels of glycolytic metabolites: glycogen, glucose, glucose-1-phosphate, glucose-6-phosphate, fructose-6-phosphate, fructose-1,6-bisphosphate, phosphoenolpyruvate, pyruvate, lactate and energetics (ATP, ADP, AMP) of livers from rats and columbian ground squirrels. Responses of adenylate pools reflected the energy imbalance created during cold hypoxia in both rat and ground squirrel liver within minutes of organ isolation. In rat, ATP levels and energy charge values for freshly isolated livers were 2.54 mol·g-1 and 0.70, respectively. Within 5 min of cold hypoxia, ATP levels had dropped well below control values and by 8 h storage, ATP, AMP, and energy charge values were 0.21 mol·g-1, 2.01 mol·g-1, and 0.17, respectively. In columbian ground squirrels the patterns of rapid ATP depletion and AMP accumulation were similar to those found in rat. In rat liver, enzymatic regulatory control of glycolysis appeared to be extremely sensitive to the decline in cellular energy levels. After 8 h cold hypoxia levels of fructose-6-phosphate decreased and fructose-1,6-bisphosphate increased, thus reflecting an activation of glycolysis at the regulatory step catalysed by phospho-fructokinase fructose-1,6-bisphosphatase. Despite an initial increase in flux through glycolysis over the first 2 min (lactate levels increased 3.7 mol·g-1), further flux through the pathway was not permitted even though glycolysis was activated at the phosphofructokinase/fructose-1,6-bisphosphatase locus at 8 h, since supplies of phosphorylated substrate glucose-1-phosphate or glucose-6-phosphate remained low throughout the duration of the 24-h period. Conversely, livers of Columbian ground squirrels exhibited no activation or inactivation of two key glycolytic regulatory loci, phosphofructokinase/fructose-1,6-bisphosphatase and pyruvate kinase/phosphoenolpyruvate carboxykinase and pyruvate carboxylase. Although previous studies have shown similar allosteric sensitivities to adenylates to rat liver phospho-fructokinase, there was no evidence of an activation of the pathway as a result of decreasing high energy adenylate, ATP or increasing AMP levels. The lack of any apparent regulatory control of glycosis during cold hypoxia may be related to hibernator-specific metabolic adaptations that are key to the survival of hypothermia during natural bouts of hibernation.Abbreviations DHAP
dihydroxyacetonephosphate
- EC
energy charge
- F1,6P2
fructose-1,6-bisphosphate
- F2,6P2
fructose-2,6-bisphosphate
- F6P
fructose-6-phosphate
- FBP
fructose-1,6-bisphosphatase
- G1P
glucose-1-phosphate
- G6P
glucose-6-phosphate
- GAP
glyceraldehyde-3-phosphate
- GAPDH
glyceraldehyde-3-phosphate dehydrogenase
- L/R
lactobionate/raffinose-based solution
- MR
metabolic rate
- PDH
pyruvate dehydrogenase
- PEP
phosphoenolpyruvate
- PEPCK & PC
phosphoenolpyruvate carboxykinase and pyruvate carboxylase
- PFK
phosphofructokinase; PK, pyruvate kinase
-
Q
10
the effect of a 10 °C drop in temperature on reaction rates (generally, Q
10=2–3)
- TA
total adenylates
- UW solution
University of Wisconsin solution (L/R-based) 相似文献
943.
944.
云南西部局限蚊属一新种:(双翅目:蚊科) 总被引:1,自引:0,他引:1
本文报道1989年8月从滇西边陲盈江县那邦河谷地带的野生芭蕉叶腋采获的一新种局限蚊--长鬃局限蚊Topomyia(T.)longisetosa sp.nov.。标本保存于云南省流行病研究所。 相似文献
945.
Kun-Ze Lee David D Fuller I-Jung Lu Jin-Tun Lin Ji-Chuu Hwang 《Journal of applied physiology》2007,102(1):434-444
Hypoglossal (XII) nerve recordings indicate that pulmonary C-fiber (PCF) receptor activation reduces inspiratory bursting and triggers tonic discharge. We tested three hypotheses related to this observation: 1) PCF receptor activation inhibits inspiratory activity in XII branches innervating both tongue protrudor muscles (medial branch; XIImed) and retractor muscles (lateral branch; XIIlat); 2) reduced XII neurogram amplitude reflects decreased XII motoneuron discharge rate; and 3) tonic XII activity reflects recruitment of previously silent motoneurons. Phrenic, XIImed, and XIIlat neurograms were recorded in anesthetized, paralyzed, and ventilated rats. Capsaicin delivered to the jugular vein reduced phrenic bursting at doses of 0.625 and 1.25 mug/kg but augmented bursting at 5 mug/kg. All doses reduced inspiratory amplitude in XIImed and XIIlat (P < 0.05), and these effects were eliminated following bilateral vagotomy. Single-fiber recordings indicated that capsaicin causes individual XII motoneurons to either decrease discharge rate (n = 101/153) or become silent (n = 39/153). Capsaicin also altered temporal characteristics such that both XIImed and XIIlat inspiratory burst onset occurred after the phrenic burst (P < 0.05). Increases in tonic discharge after capsaicin were greater in XIImed vs. XIIlat (P < 0.05); single-fiber recordings indicated that tonic discharge reflected recruitment of previously silent motoneurons. We conclude that PCF receptor activation reduces inspiratory XII motoneuron discharge and transiently attenuates neural drive to both tongue protrudor and retractor muscles. However, tonic discharge appears to be selectively enhanced in tongue protrudor muscles. Accordingly, reductions in upper airway stiffness associated with reduced XII burst amplitude may be offset by enhanced tonic activity in tongue protrudor muscles. 相似文献
946.
Kun-Ze Lee David D Fuller Li-Chu Tung I-Jung Lu Li-Chi Ku Ji-Chuu Hwang 《Journal of applied physiology》2007,102(3):878-889
Phasic bursting in the hypoglossal nerve can be uncoupled from phrenic bursting by application of positive end-expired pressure (PEEP). We wished to determine whether similar uncoupling can also be induced in other respiratory-modulated upper airway (UAW) motor outputs. Discharge of the facial, hypoglossal, superior laryngeal, recurrent laryngeal, and phrenic nerves was recorded in anesthetized, ventilated rats during stepwise changes in PEEP with a normocapnic, hyperoxic background. Application of 3- to 6-cmH(2)O PEEP caused the onset inspiratory (I) UAW nerve bursting to precede the phrenic burst but did not uncouple bursting. In contrast, application of 9- to 12-cmH(2)O PEEP uncoupled UAW neurograms such that rhythmic bursting occurred during periods of phrenic quiescence. Single-fiber recording experiments were conducted to determine whether a specific population of UAW motoneurons is recruited during uncoupled bursting. The data indicate that expiratory-inspiratory (EI) motoneurons remained active, while I motoneurons did not fire during uncoupled UAW bursting. Finally, we examined the relationship between motoneuron discharge rate and PEEP during coupled UAW and phrenic bursting. EI discharge rate was linearly related to PEEP during preinspiration, but showed no relationship to PEEP during inspiration. Our results demonstrate that multiple UAW motor outputs can be uncoupled from phrenic bursting, and this response is associated with bursting of EI nerve fibers. The relationship between PEEP and EI motoneuron discharge rate differs during preinspiratory and I periods; this may indicate that bursting during these phases of the respiratory cycle is controlled by distinct neuronal outputs. 相似文献
947.
ELOIZA A.M. DE SOUZA VALÉRIA P.R. MINIM LUIS A. MINIM JANE S.R. COIMBRA RONEY A. DA ROCHA 《Journal of sensory studies》2007,22(2):115-125
The effect of some fresh‐cut carrot label attributes on consumer purchase intention was evaluated using conjoint analysis. The following three attributes were chosen and manipulated: price (high and low), packaging type (polyethylene bags and expanded polystyrene trays) and production process (organic with certification stamp, organic without certification stamp and no information). A complete factorial design was used, and 12 hypothetical packages of fresh‐cut carrot were developed and evaluated by 96 consumers based on their purchase intention. The consumers were divided into four groups with different opinions. Low price and organic with certification label were the favorite choices of the groups. Only one group preferred expanded polystyrene trays. No interactions were exhibited among the attributes in all groups. 相似文献
948.
949.
Holt, Stanley C. (Dartmouth Medical School, Hanover, N.H.), S. F. Conti, and R. C. Fuller. Photosynthetic apparatus in the green bacterium Chloro-pseudomonas ethylicum. J. Bacteriol. 91:311-323. 1966.-When cells of Chloro-pseudomonas ethylicum were broken by ballistic disruption and examined by electron microscopy, vesicles 1,300 to 1,500 A long and 300 to 500 A wide were found to rim the periphery of the cell. Examination of these vesicles obtained by disruption with a French pressure cell and purified by density gradient centrifugation revealed inter-connections between the vesicles. During sonic and Mickle disruption of the cells, chlorophyll was released at a lower rate than soluble cytoplasmic components, but faster than the membrane-bound enzyme succinic dehydrogenase. Unlike the situation that exists in the purple photosynthetic bacteria, it appears that the chlorophyll in the green bacteria is contained as part of a structure which may be differentiated both structurally and functionally from the bacterial cytoplasmic membrane. 相似文献
950.