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51.
Juli O'Connor Dean F. Revell Karen E. Masters Ian F. Connerton Ian G. Sumner 《Protein expression and purification》1996,7(4):377-383
The gene encoding the 67-kDa cocoa storage protein precursor has been cloned fromTheobroma cacaoand expressed inEscherichia coliusing the pET expression system. The recombinant storage protein has been renatured from inclusion bodies at 30°C using 20 m
glycine–NaOH buffer, pH 10.0, containing 1 m
oxidized glutathione and 0.1% Brij. The renatured protein was purified and demonstrated to adopt a stable native conformation by optical spectroscopy. Secondary structure analysis from circular dichroism indicated the protein to be 23% α-helix and 38% β-sheet, in close agreement with values obtained using a secondary structure prediction program. 相似文献
52.
Human Microtubule-Associated Protein-2c Localizes to Dendrites and Axons in Fetal Spinal Motor Neurons 总被引:2,自引:0,他引:2
Joanna S. Albala Yvonne Kress Wan-Kyng Liu Karen Weidenheim Shu-Hui C. Yen Bridget Shafit-Zagardo 《Journal of neurochemistry》1995,64(6):2480-2490
Abstract: Microtubule-associated protein-2 (MAP-2) functions to maintain neuronal morphology by promoting the assembly of microtubules. MAP-2c is an alternately spliced form of MAP-2, containing the first 151 amino acids of high-molecular-weight (HMW) MAP-2 joined to the last 321 amino acids, eliminating 1,352 amino acids specific to HMW MAP-2. A polyclonal antibody generated to the splice site of human MAP-2c was used to determine its cellular localization. The MAP-2c antiserum was depleted of any HMW MAP-2 reactivity by absorption with HMW MAP-2 fusion protein. Western blot analysis of human fetal spinal cord homogenates demonstrated that the antibody is specific for human MAP-2c. MAP-2c immunoreactivity was found in the perinuclear cytoplasm and processes of anterior motor neurons and large processes of the posterior column in sections from 22–24-week human fetal spinal cord. Double-label confocal microscopy was performed using the MAP-2c polyclonal antibody and either a HMW MAP-2 or a neurofilament protein (highly phosphorylated 160- and 200-kDa protein) monoclonal antibody to identify these processes as dendrites or axons, respectively. HMW MAP-2 and MAP-2c colocalized in cell bodies and dendrites of anterior motor neurons, demonstrating for the first time the presence of native MAP-2c within dendrites. In addition, immunoelectron microscopy showed MAP-2c associated with microtubules in dendrites of motor neurons. MAP-2c and the neurofilament proteins were found in axons of the dorsal and ventral roots. The presence of MAP-2c within axons and dendrites suggests that MAP-2c contributes to neuronal plasticity during human fetal development. 相似文献
53.
Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) Regulation of Sympathetic Neuron Neuropeptide Y and Catecholamine Expression 总被引:4,自引:1,他引:3
Abstract: Two forms of pituitary adenylate cyclase-activating polypeptide (PACAP), the 38- and 27-amino-acid forms (PACAP38 and PACAP27, respectively), which share amino acid sequence homology with vasoactive intestinal peptide (VIP), were evaluated for their abilities to regulate sympathetic neuron catecholamine and neuropeptide Y (NPY) expression. PACAP38 and PACAP27 potently and efficaciously stimulated NPY and catecholamine secretion in primary cultured superior cervical ganglion (SCG) neurons; 100- to 1,000-fold higher concentrations of VIP were required to modulate secretion, suggesting that SCG neurons express the PACAP-selective type I receptor. PACAP38 elicited a sustained seven- to ninefold increase in the rate of NPY secretion and three-fold stimulation in the rate of catecholamine release. PACAP38 and PACAP27 produced parallel neuronal NPY and catecholamine release, but cellular levels of NPY and catecholamines were differentially regulated. Sympathetic neuron NPY content was decreased, whereas cellular total catecholamine levels were elevated by the PACAP peptides; total NPY and catecholamine levels (secreted plus cellular content) were increased. In concert with the increased total peptide and transmitter production, pro-NPY and tyrosine hydroxylase mRNA levels were elevated. Furthermore, PACAP38 was more efficacious than PACAP27 in regulating pro-NPY and tyrosine hydroxylase mRNA. SCG neuronal expression of mRNA encoding the type I PACAP receptor further supported the studies demonstrating that sympathetic neuronal levels of NPY and catecholamine content and secretion and mRNA are differentially regulated by the PACAP peptides. 相似文献
54.
Summary The thickness of the pre-epithelial mucus layer has been measured in different gut segments of rats kept under normal (ad libitum) feeding conditions, and after 48 h of fasting, using cryostat sections and celloidin stabilization from samples containing
luminal contents. The mucus layer of the stomach, duodenum, jejunum, ileum, caecum, proximal colon, colon transversum, distal
colon and rectum was studied in five groups of male rats (10, 40, 70 and 150 days of age, and older). Underad libitum feeding conditions, a distinct and continuous mucus layer, with a thickness of more than 3 μm, was only observed in the colon
transversum, in the distal colon, in the rectum and in the stomach. No pre-epithelial mucus layer was observed in the duodenum
and jejunum where the glycocalix from the apical membrane of the superficial cells appeared to be in a direct contact with
the luminal ingesta. In the ileum, caecum and the proximal colon, the surface epithelium of the mucosa was only partly covered
by a mucus layer of highly variable thickness. After 48 h of fasting, a mucus layer of 28.8 ± 25.6 μm and 93.3 ± 59.4 μm thickness,
respectively, was found in the duodenum and jejunum of adult rats, but no increase in the thickness of the mucus layer was
observed in the rat hind gut. 相似文献
55.
56.
57.
Ecological correlates of hind-limb length in the Carnivora 总被引:1,自引:0,他引:1
What determines the lengths and proportions of mammalian limbs? While the answer to this question is still largely unknown, a number of workers have recently begun analysing the selection of morphology in a rigorous framework, searching for quantitative links between structure, performance, and their ecological and behavioural context. The present study investigates a variety of ecological and behavioural variables to determine whether or not they are correlated with hind-limb length in the Carnivora. Data were analysed by using phylogenetically independent contrasts and phylogenetic analysis of covariance. We found that traditional perceptions of limb length are often inaccurate; some species widely regarded as relatively long-legged actually have limb lengths near those expected for their body size. Interestingly, relative hind-limb length is not a significant predictor of distance moved daily, home-range area, or prey size. Phylogenetic ANCOVA results, however, indicate a relationship between prey-capture behaviour and relative hind-limb length. These findings suggest that the evolution of carnivoran limb length has been most influenced by selection for prey-capture behaviour. These results, coupled with those of other studies, can be used to suggest which performance variables could most fruitfully be studied in the laboratory to understand the selection of the structure of the mammalian limb. We suggest that relevant performance variables might be: maximum jump height and/or length, the ability to generate outforces, and levels of stress tolerance in limb bones during prey pursuit/capture. 相似文献
58.
Posttetanic potentiation of human dorsiflexors 总被引:2,自引:0,他引:2
O'Leary, Deborah D., Karen Hope, and Digby G. Sale.Posttetanic potentiation of human dorsiflexors.J. Appl. Physiol. 83(6):2131-2138, 1997.Twitch contractions of the ankle dorsiflexors were evoked before and after applied 7-s tetanic stimulation at 100 Hzin 20 young adults. Torque decreased 15% during the tetanus. At 5 safter tetanus, twitch peak torque had potentiated 45%. Potentiationdeclined to 28% after 1 min, rose slightly to 33% at 2 min, anddeclined slowly with potentiation still 25% after 5 min. There waslarge intersubject variation in the amount of potentiation(5-140%) and its persistence (5 to 20 min). The muscle compoundaction potential (M wave) did not change significantly (from pretetanicvalue) at 5 s after tetanus but increased sharply (26%) at 2 min andthen subsided. Twitch half relaxation time (23%) decreasedsignificantly more than twitch rise time (13%) 5 s after tetanus andrecovered more slowly. Twitch rates of torque development (75%) andrelaxation (71%) increased similarly 5 s after tetanus and were stillelevated (~25%) at 5 min. The extent of twitch torque potentiationwas significantly inversely correlated with pretetanic twitch rise time(r = 0.69), half relaxation time (r = 0.61), andtwitch-to-tetanus ratio (r = 0.66). The data indicate that posttetanic potentiation has agreater effect on twitch half relaxation time than on time to peaktorque and is more prominent in muscles with a short twitch time courseand small twitch-to-tetanus ratio. 相似文献
59.
Dr. Mark E. McKinney Karen Rovang Dr. James C. Buell Dr. Robert S. Eliot 《Applied psychophysiology and biofeedback》1984,9(3):365-370
Impedance cardiography (ZCG), a noninvasive technique used to determine stroke volume and ventricular performance, is currently being utilized more extensively in psychophysiological research and may also prove a useful tool in the control of hypertension. To date, most studies employing ZCG have tested male subjects or patients. However, women and men differ on two important parameters used to calculate stroke volume: thoracic impedance (Zo), and the first derivative of change in impedance over time (dZ/dtmin). Examination of the clinical records of 19 females and 19 males, all nonmedicated, indicated that women had higher Zo levels (F(1, 36)=46.2,p<.0001) and higher dZ/dtmin levels (F(1, 36)=51.8, p<.0001), although calculated stroke volume indexes did not differ. A second sample of 10 women and 8 men, all healthy and nonmedicated, confirmed these findings. The differences in Zo are not due entirely to sex differences in height, weight, percent body fat, and subscapula skin-fold thickness, although these factors differ across sexes. It is important for researchers and clinicians utilizing ZCG with female subjects to be aware of these differences. 相似文献
60.
We have examined the shape and distribution of clathrin-coated pits in Swiss 3T3 cells at 4 or 37 degrees C using electron microscopy with serial sections and immunofluorescence light microscopy. Both groups were fixed in glutaraldehyde and preserved further using a membrane contrast enhancement technique consisting of sequential osmium-ferrocyanide, thiocarbohydrazide and osmium-ferrocyanide treatment in situ. Concanavalin A-horseradish peroxidase (conA-HRP) was used to identify these structures participating in endocytosis. Two hundred twenty-two clathrin-coated structures were analysed; 126 from cells fixed at 4 degrees C, and 96 from cells fixed after a 3 min warm-up to 37 degrees C. All coated structures labeled with conA-HRP had demonstrable connections to the plasma membrane. These coated structures were morphologically classified into three categories: (a) flat pits; (b) curved pits; and (c) pits with narrow-neck connections to the plasma membrane. At 37 degrees C, 27% of coated pits had narrow neck connections to the plasma membrane whereas at 4 degrees C only 1% had such connections. Receptosomes (endosomes) labeled with conA-HRP were found only after incubation at 37 degrees C, indicating that active endocytosis was occurring in cells at 37 degrees C, but not at 4 degrees C. Immunofluorescence with anti-clathrin antibody was used to quantitate the number of clathrin-coated pits in Swiss 3T3 cells incubated at 4 and 37 degrees C prior to fixation. No difference was detected. There were 426 +/- 122 pits per cell at 37 degrees C and 441 +/- 106 at 4 degrees C. These results support the hypothesis that formation of a narrow neck connected a coated pit to the cell surface is an early step in the mechanism of receptor-mediated endocytosis. 相似文献