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71.
Global stability of stationary solutions to a nonlinear diffusion equation in phytoplankton dynamics
We consider a nonlinear diffusion equation proposed by Shigesada and Okubo which describes phytoplankton growth dynamics with a selfs-hading effect.We show that the following alternative holds: Either (i) the trivial stationary solution which vanishes everywhere is a unique stationary solution and is globally stable, or (ii) the trivial solution is unstable and there exists a unique positive stationary solution which is globally stable. A criterion for the existence of positive stationary solutions is stated in terms of three parameters included in the equation. 相似文献
72.
A new rapid and simple method has been developed for the separation of disaccharides obtained by chondroitinase digestion of chondroitin sulfates and dermatan sulfate using electrophoresis on cellulose acetate plates (Titan III cellulose acetate plates). Three disaccharides are completely separated by electrophoresis in barium acetate or calcium acetate in a short time, and less than 50 μg of glycosaminoglycan samples can be analyzed within 2 h. 相似文献
73.
The ubiquinone protein, QP-C, in reduced ubiquinone-cytochrome c reductase (the b?c1-III complex) shows a stable ubisemiquinone radical when the enzyme is reduced by succinate in the presence of catalytic amounts of succinate dehydrogenase and QP-S. At room temperature using EPR technique the redox titration of the b?c1-III complex in the presence of redox dyes or succinate/fumarate couple reveals that the ubisemiquinone radical has a midpoint potential of approximately +67 mV at pH 8.0. Further analysis yields E1 of +83 mV and E2 of +51 mV corresponding to () and () or other electronated forms, respectively. The equilibrium radical concentration has been found to be affected both by pH and succinate/fumarate couple. At pH 9.0 the radical shows the maximal amplitude and stability. Below pH 7.0, little radical was detected. The electron spin relaxation behavior of ubisemiquinone radical, as examined by microwave power saturation, indicates that the ubisemiquinone radical of QP-C is somewhat isolated from other paramagnetic centers. The effects of phospholipids, QP-S, and other agents on ubisemiquinone radical formation as well as the enzymatic activity of QP-C have been studied in detail. 相似文献
74.
5′-Nucleotidase (EC 3.1.3.5) was solubilized from rod membranes with Ammonyx LO and purified by chromatographic methods. A highly sensitive radioassay was developed. The purified enzyme behaved as a homogeneous protein of 75,000 daltons in sodium dodecyl sulfate-polyacrylamide gel electrophoresis and as a protein of 79,000 in gel filtration. Thus, the enzyme does not contain subunits. The Km values obtained were 1.3 μm for 5′-AMP and 2.3 μm for 5′-GMP. The enzyme was inhibited by concanavalin A, wheat germ agglutinin, and Ricinus communis agglutinin. Rabbit muscle G-actin formed a complex with the enzyme and inhibited its activity. The catalytic site of the enzyme was localized on the internal surface of the disk which, in terms of membrane sidedness, corresponds to the cell surface. A soluble 5′-nucleotidase was extracted from rod membranes with Tris buffer (pH 8.0) containing EGTA in the dark; less enzyme was extracted if the membranes had been exposed to light or incubated with Ca2+. The extracted enzyme was partially purified. The enzyme was unstable and lost 50% of its activity in 3 days at 3 °C. The Km values were 1.3 μm for 5′-AMP and 2.3 μm for 5′-GMP. The enzyme was inhibited by G-actin. A role for the soluble enzyme in the regulation of 5′-GMP in the rod outer segment was suggested. 相似文献
75.
Controlled alkaline hydrolysis of 16α-bromo-17-keto steroids , and with potassium carbonate and tetra-n-butylammonium hydroxide (n-Bu4NOH) and synthesis of 2α-hydroxy-3-ones , and by the controlled hydrolysis of the corresponding 2α-bromo-3-ones , and are described. Treatm carbonate in aqueous acetone or with n-Bu4NOH in aqueous dimethylformamide (DMF) gave 16α-hydroxy-17-ones , and in 85–90% yield, respectively. 2α-Hydroxy-3-ones , and were obtained by hydrolysis of the corresponding bromoketones , and in high yields using the above conditions or sodium hydroxide in pyridine or DMF, respectively. Deuterium labeling experiments suggested that equilibration between the 2α-bromoketone and the 2β-bromo isomer precedes the formation of the ketol in which the true intermediate might be the 2β-isomer . However, rearranged androstane derivatives, 3β-hydroxy-2-ones and , were stereoselectively obtained by treatment of the bromoketones and with an excess amount of sodium hydroxide. 相似文献
76.
Eggs of Oryzius latipes in the blastula stage were exposed to M/100 artificial sea water which contained cadmium at the concentrations of 0.1, 1.0, 10.0, 20.0 or 50.0 mg 1−1 . The 96 h TL50 , value for cadmium was estimated to be 20 5 mg 1−1 . When the eggs were incubated for 24 h in the M/100 sea water with 10.0 mg Cd 1−1 and then rinsed in glycine buffer solution (pH; 2.0), the cadmium content of the egg decreased markedly. Cadmium levels were determined in parts of the embryonic body, the chorion and the yolk sac. The most cadmium was detected in the chorion (94.6%). Prolonged cadmium exposure revealed that most of the cadmium was absorbed by the chorion and little was detected in the embryonic body and the yolk sac. 相似文献
77.
Triton X-100 extract from brush border membranes of rat small intestine was recombined with egg phosphatidylcholine liposomes by the freeze-thaw sonication method. The treated liposomes showed a Na+-dependent uptake of cyclacillin, which was inhibited by a low concentration of mercuric ions and L-phenylalanylglycine, but not by glycine. These are consistent with the absorption characteristics of the antibiotic in situ and indicate that reconstitution of the Na+-dependent active cyclacillin transport system of rat small intestine has been achieved. 相似文献
78.
NG, a strain of cultured tobacco cells of Nicotiana glutinosahad high growth rates and carboxylate contents (CA) of100 to 130 meq/100 g of dry cells on media containing 42 meqNO3/liter as the sole N source. (CA) is the amount ofinorganic cations minus inorganic anions in meq per 100 g ofdry cells. NG, cultured on media containing NH4 10+NO3 42 in meq/liter,had lower growth rates and lower (CA) values as comparedwith NG on media containing NO3 as the sole N source. NG, cultured on media containing NH4 30+NO3 42 in meq/liter,had high growth rates and (AC) values of 22 to 53 meq/100gof dry cells. In this case, the (AC) content may correspondto organic cations, basic organic N compounds such as free asprotein-bound basic amino acids. The easily absorbed Cl mayhave been required maintain good growth conditions such as ionicbalance and a favorable pH in the cells. Thus cultured cells of Nicotiana glutinosa may have physiologicaladaptability against variations in a relatively wide range of|CA| contents [|CA| being the absolute valuesof (CA)]. (Received May 15, 1980; ) 相似文献
79.
Noriyuki Muranushi Noriko Takagi Shozo Muranishi Hitoshi Sezaki 《Chemistry and physics of lipids》1981,28(3):269-279
The effect of fatty acids and monoglycerides on barrier properties of liposomal membranes prepared from egg phosphatidylcholine was investigated. The incorporation of these lipids as liposomal membrane components induced the alteration of the permeability to less permeable liposomally entrapped drugs, sulfanilic acid and procainamide ethobromide (PAEB). Monoolein caused greatly increased permeability of both drugs and unsaturated fatty acids markedly enhanced the release rate of PAEB, while saturated fatty acids caused a small increase in the release rate.Electron spin resonance (ESR) investigation with 5-nitroxide stearic acid showed that fatty acids disordered the hydrophobic region of the lipid bilayer and the disordering effect of unsaturated fatty acids was greater than that of saturated ones. It was demonstrated that the incorporated fatty acids and monoglycerides interacted with the polar region of the membranes by ESR study with cholestane label and 1H-NMR study. These results indicated that the increase in the membrane permeability caused by fatty acids and monoglycerides associated with the disorder in the membranes' interior and the interaction of the incorporated lipid with the polar head group of phospholipid. 相似文献
80.
Hitoshi Iizumi Akihiko Hattori C.P. McRoy 《Journal of experimental marine biology and ecology》1980,47(2):191-201
The distribution of nitrate and nitrite in the interstitial water of the sediment of eelgrass (Zostera marina) bed of Izembek Lagoon, Alaska, were investigated. Their concentrations were relatively high (0 to 9.8 μg-at.N·1?1, average 4.8 for nitrate; 0 to 4.0 μ-at.N·1?1, average 1.9 for nitrite) although the sediments were anoxic and contained hydrogen sulphide. The rates of bacterial denitrification measured by 15N tracer technique ranged from 0.49×10?10 to 1.2 × 10?9 g-atN·g?1·h?1. When a steady state is maintained, the loss of nitrate and nitrite must be balanced by their production by bacterial nitrification. Experimentally determined rate of nitrification in the sediment was of the same order. A model experiment demonstrated that oxygen is transported from leaves to rhizomes and roots of eelgrass and released into the sediment. The oxygen is used for nitrification in the rhizosphere in anoxic sediments. 相似文献