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991.
The conformational energy of a molecule is minimized with respect to interatomic distances using Bremermann's method of unconstrained global optimization (1970). The optimal set of distances is then used for calculating the preferred conformation of the molecule. A simultaneous optimization of all the dihedral angles is achieved. The classical potential function is used in this study. An illustration of the method is given by applying it to normal pentane, which is a commonly occurring fragment of biomolecules. Results show that, for the standard geometry (bond lengths and bond angles), the all-trans) conformation is the preferred one. However, fluctuations of the geometry within the limits of the vibrational spectra can lead to preferred conformations that are not necessarily all-trans. 相似文献
992.
Kevin W. Park Anil K. Tyagi David A. Cooney 《Journal of biochemical and biophysical methods》1980,2(5):291-297
When radioactive adenylsuccinic acid (AMP-S) is metabolized to AMP and fumaric acid by the enzyme adenylsuccinate lyase (EC 4.3.2.2), a proton is released to the solvent as 3H2O. This removal is believed to be stereospecifically identical to that catalyzed by the enzyme, l-aspartase [1–5], and therefore entails the loss of a proton from C-3 of the dicarboxylic acid moiety of the nucleotide. Advantage has been taken of this fact in the design of a facile assay for this enzyme. Adenylosuccinic acid, tritiated on C-2 and C-3 of the l-aspartase moiety, is prepared by chemical synthesis. This product is purified, lyophilized to dryness and reconstituted in a solution of unlabelled AMP-S, bringing the final concentration to 5·10?3 M, and the final specific activity to 8.0 μCi/mol. 5-μl aliquots of this substrate are then incubated at 37°C with 5-μl aliquots of tissue extract; after an appropriate period, any tritium released to the solvent water is distilled at room temperature overnight into a 5 μl droplet of saturated aqueous KOH adherent to the lid of the sealed reaction vessel. The lid is removed and tritium thereon is measured by scintillation spectrometry. The assay, performed as prescribed, is facile, in that it permits the simultaneous estimation of the lyase activity in a large battery of samples, is not interfered with by opalescent or proteinaceous suspensions, is accurate and outstandingly sensitive. 相似文献
993.
994.
Motomi Katada Somdev Tyagi Amar Nath Richard L. Petersen Raj K. Gupta 《Biochimica et Biophysica Acta (BBA)/General Subjects》1979,584(1):149-163
A new isomeric form of cobalamins is reported. The conversion of cobalamin to cobalamin′ (the new form) is achieved by substituting the benzimidazole base by a less bulky group like H2O of CN? and modest thermal treatment. The back conversion of adenosylcobalamin′ to the corresponding regular form occurs in the ‘base-off’ form at room temperature. It seems that the corrin ring becomes quite flexible in the ‘base-off’ form and the freer axial movement of the cobalt atom flips the corrin ring into a different conformation. The change in conformation is borne out by subtle changes in the proton magnetic resonances on the corrin ring and the base, and very marked variation in the emission Mössbauer spectra. The latter is indicative of appreciable changes in the spatial conformation in the immediate vicinity of the central metal atom.The ultraviolet-visible and infrared spectra of a cobalamin′ are indistinguishable from those of its corresponding regular form.The new conformational isomeric species is present as an impurity in all commercially available cobalamins (including pharmaceutical preparations). It raises the question whether the cobalamins′ constitute the real biologically active anti-anemic factor in humans 相似文献
995.
Himani Anand M. M. Misro S. B. Sharma Sant Prakash 《Apoptosis : an international journal on programmed cell death》2012,17(11):1131-1143
Using siRNA as a tool, the channelization of pathway in H2O2 induced apoptosis of primary Leydig cells was investigated in vitro. Exposure (4?h) to H2O2 (250?μM) induced maximum apoptosis but affected Leydig cell viability significantly. Therefore, expression of apoptotic marker genes, caspase-8, -9, -3 and polyadenosine ribose polymerase was subsequently investigated using the same concentration post 1?h exposure. Incubation with siRNA (20?nM) either for caspase-8 or -9, inhibited their individual expressions by 55–60?% and activity, 50–55?%. The inhibition efficiency using siRNA was comparable with post- or pre-H2O2 treatment of cells. Like siRNA, Eugenia jambolana (100?μg/ml) plant extract too, effectively countered over-expression of all apoptotic marker proteins. Silencing expressions of caspase 8 but not 9 through siRNA leads to a profound inhibition of caspase 3 implying that H2O2 induced Leydig cell apoptosis is preferably channeled through extrinsic and later extending to other pathways. 相似文献
996.
Pollen embryos of Datura innoxia Mill are produced in larger numbers from anthers on agar-gelled medium containing polyvinylpolypyrrolidone than on control. The best response is observed with 0.5% polyvinylpolypyrrolidone. The effect is possibly due to adsorption of substances (phenolics) emanating from cultured anthers and inhibiting the development of pollen grains into embryos. 相似文献
997.
998.
Metabolic syndrome, insulin resistance, prediabetes, and overt type 2 diabetes mellitus are associated with an accelerated atherosclerosis (atheroscleropathy). This quartet is also associated with multiple metabolic toxicities resulting in the production of reactive oxygen species. The redox stress associated with these reactive oxygen species contribute to the development, progression, and the final fate of the arterial vessel wall in prediabetic and diabetic atheroscleropathy. The prevention of morbidity and mortality of these intersecting metabolic diseases can be approached through comprehensive global risk reduction. 相似文献