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31.
Nanosecond laser flash photolysis has been used to produce and identify the vitamin K semiquinone (radical) from vitamin K dihydroquinone and to observe its formation and decay in the presence of vitamin K-dependent carboxylase (epoxidase). The activity of vitamin K-dependent carboxylase is not decreased by exposure to the laser. Absorbance of the semiquinone is proportional to enzyme concentration and is stimulated by a synthetic substrate, PheLeuGluGluIle. Stabilization of the semiquinone is observed in the presence of the enzyme. The semiquinone is rapidly destroyed in the presence of inhibitors of vitamin K-dependent carboxylase and vitamin K epoxidase. 相似文献
32.
N-demethylation of p-chloro-N-methylaniline catalyzed by subcellular fractions from the avocado pear (Persea americana) 总被引:2,自引:0,他引:2
Subcellular fractions from the avocado pear ( Persea americana) catalyzed formation of p-chloroaniline from p-chloro-N-methylaniline. Fractions prepared by centrifugation of avocado homogenates at 20, 000g for 20 min formed p-chloroaniline (2900 +/- 500 pmol min-1 mg protein-1) with an NADPH-generating system. p-Chloroaniline formation required reduced pyridine nucleotide (NADPH was 6-7 times more effective than NADH) and O2. N-Demethylation was inhibited by CO (55% inhibition at CO:O2 = 1) and was not inhibited by CN. Cytochrome P-450 was detected in the 20, 000g pellet at levels of 300-380 pmol/mg protein. This particulate preparation was also active in catalyzing the NADPH-dependent epoxidation of the chlorinated cyclodiene aldrin. Improvements to a colorimetric procedure for measuring p-chloroaniline increased the sensitivity of the procedure fourfold, and allowed use of samples containing high amounts of lipid. Avocado pear is suitable tissue for further studies on the oxidation of foreign compounds by higher plants. 相似文献
33.
Stimulation of phospholipase A2 activity by high osmotic pressure on cholesterol-containing phospholipid vesicles 总被引:1,自引:0,他引:1
Bovine serum albumin conjugates of guanosine prepared by the periodate method was used as immunogen to elicit guanosine antibodies in rabbits. The specificities of the antibodies were studied by the inhibition of their binding to [3H]Gox-red, [32P]DNA and [3H]RNA by related non-radioactive compounds. A population of antibodies is specific to Gox-red with an average association constant of around 10(7) M-1 at 4 degrees C. There are a population of antibodies which bind to [32P]ssDNA and [3H]RNA specifically at guanosine residues. RNA binding antibodies were separated into two populations by affinity chromatography. 相似文献
34.
R.L. Horst B.C. Pramanik T.A. Reinhardt S.-J. Shiuey J.J. Partridge M.R. Uskokovic J.L. Napoli 《Biochemical and biophysical research communications》1982,106(3):1006-1011
23,25-Dihydroxyvitamin D3 was isolated from the plasma of vitamin D3-toxic pigs. An ultraviolet absorbance spectrum confirmed its purity. The configuration of the 23-hydroxyl group was determined to be S by comparison of the natural product with synthetic 23,25- and 23,25-dihydroxyvitamin D3 by high-pressure liquid chromatography. The affinity of both 23,25- and 23,25-dihydroxyvitamin D3 for the plasma vitamin D binding protein was similar to vitamin D3. Thus, with respect to the plasma vitamin D binding protein, 23,25-dihydroxyvitamin D3 is the least potent, naturally-occurring, dihydroxylated vitamin D3 metabolite known. 相似文献
35.
Life tables were constructed to assess the relative importance of some factors causing mortality of Tribolium confusum and to gauge their response to increasing population density. Observations focussed on three population densities (100, 400 and 800 individual/8 g medium) from the egg to the adult stage. The medium was not renewed in order to maximize predatory interactions. Generation mortality at densities 100, 400 and 800 was 42%, 50% and 74% respectively, i. e. density-dependent. Mortality in the first 10 days was also density-dependent reaching a maximum of 27% at density 800: predation by small larvae on eggs seemed the principal causative factor. The overall pattern of larval mortality was density-independent. Data on the mortality of pupae and callows were ultimately consistent with an inversely density-dependent pattern. Apparently, only mortality occurring within the first 10 days was capable of population regulation. 相似文献
36.
Timothy A. Reinhardt Ronald L. Horst E.Travis Littledike Donald C. Beitz 《Biochemical and biophysical research communications》1982,106(3):1012-1018
1,25-Dihydroxyvitamin D3 [1,25-(OH)2D3] receptor was characterized after partial purification of thymus cytosol by ammonium sulfate fractionation. The 1,25-(OH)2D3 receptor sediments at 3.7S in 5–20% sucrose gradients. The binding of 1,25-(OH)2D3 in thymic cytosol was a saturable process with high affinity (Kd = 0.12?0.48 nM) at 4°C. Competition for 1,25-(OH)2[3H]D3 receptor by nonradioactive analogs demonstrated the affinities of these analogs to be in order; 1,25-(OH)2D3 = 1,24R,25-(OH)3D3 = 1,25S,26-(OH)3D3 = 1,25R,26-(OH)3D3 > 1,25-(OH)2D3-26,23 lactone > 25-OHD3 > 23R,25-(OH)2D3 > 24R,25-(OH)2D3 > 23S,25-(OH)2D3 ? 25-OHD3-26,23 lactone. The receptor bound to DNA cellulose columns in low salt buffer and eluted as a single peak at 0.21 M KCl. These findings provide evidence that the thymus possesses a 1,25-(OH)2D3 receptor with properties indistinguishable from 1,25-(OH)2D3 receptors in other tissues. 相似文献
37.
38.
Jill E. Maddison Wendy E. J. Watson Peter R. Dodd Graham A. R. Johnston 《Journal of neurochemistry》1991,56(6):1881-1888
Excitatory amino acid receptor binding parameters were investigated in a spontaneous dog model of chronic hepatic encephalopathy. L-[3H]Glutamate, (+)-[3H]-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-im ine maleate ([3H]MK-801), [3H]kainate, and alpha-[3H]-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid ([3H]AMPA) binding experiments were performed using crude cerebrocortical synaptosomal membrane preparations from dogs with congenital portosystemic encephalopathy (PSE) and control dogs. There was no change in the affinity or density of L-[3H]-glutamate or [3H]MK-801 binding sites in dogs with congenital PSE compared with control dogs. However, in the PSE dogs there was a significant reduction in the density of [3H]kainate binding sites compared with control dogs and abolition of the low-affinity [3H]AMPA binding site. The relative binding capacity of PSE synaptosomal membranes for [3H]kainate and [3H]AMPA was expressed as the ratio Bmax/KD. There was a significant inverse correlation between the Bmax/KD ratio for [3H]AMPA binding and the worst grade of encephalopathy experienced by each dog. These results suggest that there is a significant perturbation of cerebrocortical non-N-methyl-D-aspartate receptor binding in dogs with congenital PSE which may have relevance to the pathogenesis of hepatic encephalopathy. 相似文献
39.
Nanako Shigesada 《Journal of mathematical biology》1980,9(1):85-96
Summary A mathematical model for the dispersal of an animal population is presented for a system in which animals are initially released in the central region of a uniform field and migrate randomly, exerting mutually repulsive influences (population pressure) until they eventually become sedentary. The effect of the population pressure, which acts to enhance the dispersal of animals as their density becomes high, is modeled in terms of a nonlinear-diffusion equation. From this model, the density distribution of animals is obtained as a function of time and the initial number of released animals. The analysis of this function shows that the population ultimately reaches a nonzero stationary distribution which is confined to a finite region if both the sedentary effect and the population pressure are present. Our results are in good agreement with the experimental data on ant lions reported by Morisita, and we can also interpret some general features known for the spatial distribution of dispersing insects. 相似文献
40.