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Andrew Porter 《BMJ (Clinical research ed.)》1981,283(6293):725-726
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Abstract— The amount of α-melanocyte-stimulating hormone (α-MSH) in the entire hypothalamus as well as the amount of α-MSH in free granule and synaptosome fractions of hypothalamic homogenates was investigated throughout the lifespan of female rats (1-24 months). A 900 g supernatant fluid was prepared from hypothalami following homogenization in an iso-osmotic sucrose solution, and free granules and synaptosomes containing α-MSH were fractionated by means of continuous sucrose density gradient centrifugation. α-MSH was quantified by radioimmunoassay. The total amount of α-MSH in the hypothalamus, as well as the amount in free granules and synaptosomes prepared from hypothalami increased progressively from the 1st to the 5th month of life, and this increase was more pronounced in the free granules than in the synaptosomes. On the other hand, the amount of α-MSH in the hypothalamus and the amount present in free granules and synaptosomes prepared from 5-24-month-old animals decreased with age, and this decrease appeared to proceed at similar rates in both subcellular compartments. Based on these results, it is suggested that ageing of α-MSH neurons in the hypothalamus is accompanied by a degeneration of the axons and/or an alteration in the biosynthetic and degradative activities of the neuron. 相似文献
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The extraction and purification of phytofluene from tomatoes is described. The purity of the best preparations obtained is approximately 25% higher than previously reported (2). The present light-absorption value for the longer wavelength maximum is that expected by extrapolation of the values obtained for ζ- and δ-carotenes, tetrahydrolycopene, and lycopene. 相似文献
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Protein domains are conspicuous structural units in globular proteins, and their identification has been a topic of intense biochemical interest dating back to the earlier crystal structures. Numerous disparate domain identification algorithms have been proposed, all involving some combination of visual intuition and/or structure-based decomposition. Instead, we present a rigorous thermodynamically based approach that redefines domains as cooperative chain segments. In greater detail, most small proteins fold with high cooperativity, meaning that the equilibrium population is dominated by completely folded and unfolded molecules, with a negligible subpopulation of partially folded intermediates. Here, domains are equated to chain segments that retain full cooperativity when excised from their parent structures. Implementing this approach computationally, the domains in a large representative set of proteins were identified; all exhibit consistency with experimental findings. Our reframed interpretation of a protein domain transforms an indeterminate structural phenomenon into a quantifiable molecular property, grounded in solution thermodynamics. 相似文献
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Three sandwich-ELISAs, two of which are commercially available (Tecra and Locate), and one developed at the Veterinary Sciences Division, Stormont and a 3-step culture protocol, were compared for the detection of salmonella in 1000 animal specimens. Eight hundred and fifty of these were new submissions and the remainder were frozen portions from specimens previously shown to contain salmonellas by culture. The incidence of ELISA false-negative and false-positive results was highest for the Stormont and Locate kits respectively although the differences in sensitivity and specificity between the three ELISAs was not statistically significant. On 16 occasions all ELISA methods indicated the presence of salmonellas when none were isolated by initial culture, eight of these specimens contained salmonellas when reinvestigated by culture. 相似文献
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A A Qureshi A G Andrewes N Qureshi J W Porter 《Archives of biochemistry and biophysics》1974,162(1):93-107
This paper reports the conversion of cis-[14C]phytofluene to trans-[14C|phytofluene and the conversion of the latter compound to trans-ζ-[14C]carotene by a soluble enzyme system obtained from the plastids of red tomato fruits. Each of these radioactive compounds was also converted to labeled neurosporene, lycopenc, α-carotene, and β-carotene by the same enzyme system. The incorporation of each substrate into more unsaturated carotenes was carried out under nitrogen at pH 7.5–8.2 (borate buffer), at 25 °C in the dark.Proof of the formation of the above carotenes from each of the three radioactive substrates was demonstrated by cochromatography with authentic nonradioactive carotenes on an alumina chromatographic column. A close correspondence between radioactivity and light absorbance for each carotene was observed. Confirmation of these conversions was achieved by cochromatography with authentic samples on thinlayer plates. Final proof for the formation of the acyclic and cyclic carotenes from the above radioactive substrates was obtained by gas-liquid chromatography of the hydrogenated products. Coincidence between mass and radioactivity was observed.Maximum conversion of cis- and trans-phytofluenes to more unsaturated carotenes by the red tomato fruit enzyme system appears to be dependent upon the presence of NADP+, FAD, and Tween 80. The formation of the carotenes is also increased in the presence of Mg2+ or Mn2+ ions. 相似文献