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51.
52.
The carcinogen, 7,12-dihydroxymethylbenz[alpha]anthracene (DHBA), was regioselectively conjugated in the presence of 3'-phosphoadenosine 5'-phosphosulfate by male rat liver cytosolic sulfotransferase to DHBA 7-sulfate. The sulfate ester was highly reactive and showed a potent, intrinsic mutagenicity toward Salmonella typhimurium TA 98.  相似文献   
53.
Nitrate reductase was purified about 3,000-fold from spinach leaves by chromatography on butyl Toyopearl 650-M, hydroxyapatite-brushite, and blue Sepharose CL-6B columns. The purified enzyme yielded a single protein band upon polyacrylamide gel electrophoresis under nondenaturing conditions. This band also gave a positive stain for reduced methylviologen-nitrate reductase activity. The specific NADH-nitrate reductase activities of the purified preparations varied from 80 to 130 units per milligram protein. Sucrose density gradient centrifugation and gel filtration experiments gave a sedimentation coefficient of 10.5 S and a Stokes radius of 6.3 nanometers, respectively. From these values, a molecular weight of 270,000 ± 40,000 was estimated for the native reductase. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the denatured enzyme yielded a subunit band having a molecular weight of 114,000 together with a very faint band possessing a somewhat smaller molecular weight. It is concluded that spinach nitrate reductase is composed of two identical subunits possessing a molecular weight of 110,000 to 120,000.  相似文献   
54.
The cadaverine content of soybean radicles showed a maximumpeak 3–4 days after planting. The variation coincidedwith radicle uricase activity during seed germination. The uricase activity could not be fractionate when the bufferpH for the extraction was at 6.0. The addition of 1 M KCl orNaCl to the buffer allowed the extraction of the uricase activity,but an addition of 1 M MgCl2 or BaCl2 inhibited this enzyme'sactivity. The urate-degrading enzyme system was purified 248-fold permilligram of protein from soybean radicles. The respective Kmvalues of the diamine oxidase activity for cadaverine and ofthe urate-degrading activity for hydrogen peroxide and uratewere 1.25, 2.93 and 50.3 µM. Analysis by gel electrophoresisof the partially purified enzyme fraction revealed that theurate-degrading enzyme system consisted of a peroxidase thatdegrades urate with hydrogen peroxide and a diamine oxidasethat releases hydrogen peroxide. These data are evidence that a urate-degrading diamine oxidaseand peroxidase system exists in soybean radicles and that thereaction rate of urate-degradation is controlled by the concentrationof cadaverine. (Received November 28, 1984; Accepted April 8, 1985)  相似文献   
55.
Inhibition of photosynthesis by Na2SO3 in mesophyll protoplastsisolated from Vicia faba leaves and uptake of sulfite by theprotoplasts were examined at various pH values of the incubationmedium containing Na2SO3. As the pH of the incubation mediumlowered, the rate of photosynthesis in the protoplasts decreasedand the amount of sulfite taken up by the protoplasts increased.Most of sulfite accumulated in the protoplasts was not metabolizedduring the dark incubation, as measured with an ion chromatograph.Photosynthetic O2 evolution by the chloroplasts isolated fromVicia mesophyll protoplasts was inhibited by exogenously-appliedNa2SO3 over pH region examined (7.4–9.0). The sulfiteconcentration required for a half inhibition of photosynthesisby the isolated chloroplasts was similar to the intracellularsulfite level required for that by the protoplasts. These resultsindicate that the intracellular sulfite accumulated in the protoplastsin an unmetabolized state is responsible for the inhibitionof protoplast photosynthesis. (Received January 24, 1985; Accepted May 29, 1985)  相似文献   
56.
Cell suspensions were initiated from plumule derived calli ofSpinacia oleracea. Some of these cell lines could be maintained in culture for at least three years without a reduced growth rate. A high yield of protoplasts was obtained from the cell suspensions. When protoplasts were cultured in Murashige and Skoog medium with naphthaleneacetic acid and 6-benzyladenine, cell wall formation was observed after three days. The cultured protoplasts produced numerous cell-clusters within two weeks. However only protoplasts isolated from suspensions which were in a rapidly dividing phase were able to divide with a high frequency and give rise to callus colonies.  相似文献   
57.
Two hundred and twenty species of 38 genera in the Cyperaceae from Australia were examined for the possible occurrence of the C4 photosynthesis and the anatomical features of leaves and culms. The Kranz type of anatomy and the carbon isotope ratios typical of C4 plants were found in 84 species in the following six genera of four tribes belonging to subfamily Cyperoideae:Bulbostylis, Crosslandia, andFimbristylis (Fimbristylideae);Lipocarpha (Lipocarpheae);Cyperus (Cypereae);Rhynchospora (Rhynchosporeae). The anatomical observation revealed that the C4 species possessed any one of the three Kranz anatomical types found by previous investigators. It was suggested that in the Cyperaceae the C4 syndrome evolved independently within several taxa of the subfamily. The relative distribution of C3 and C4 species of the Cyperaceae in Australia was investigated by use of floristic data. It was recognized that the C4 species dominated in the northern part of the continent which was characterized by tropical and subtropical savannas and hot dry areas with summer rainfall, and the C3 species in the southern part, which contained temperate areas and mediterranean climatic areas with winter rainfall.  相似文献   
58.
In an attempt to elucidate the relationship between phosphatidylinositol breakdown and alpha-adrenergic responses, effects of phosphatidic acid and phosphatidylinositol related metabolites on Ca2+ mobilization and glucose output in cultured hepatocytes were examined. Norepinephrine induced the net 45Ca2+ efflux from preloaded cells and stimulated glucose output via alpha-adrenergic receptor stimulation, whereas phosphatidic acid caused 45Ca2+ uptake to cells and did not stimulate glucose output. Myo-inositol-monophosphate, diglyceride and arachidonic acid, which are released by phosphatidylinositol breakdown, had no effect on 45Ca2+ efflux and glucose output in cells. These results suggest that phosphatidic acid and phosphatidylinositol related metabolites can not mimic the alpha-adrenergic actions in cultured hepatocytes.  相似文献   
59.
Three oleanane triterpenes were isolated from the roots of Periandra dulcis,and identified as 3β-hydroxy-25-al-olean-18-en-30-oic acid (periandric acid I), 3β-hydroxy-25-al-olean-12-en-30-oic acid (periandric acid II) and 3-oxo-25-hydroxy-olean-12-en-30-oic acid. The former two compounds (periandric acids I and II) were identical with the aglycones obtained by hydrolysis of periandrin I and II, respectively and the latter one was a new triterpene.  相似文献   
60.
The recent model of Kambara and Govindjee for water oxidation [Kambara T. and Govindjee (1985) Proc. Natl. Acad. Sci. U.S.A., 82:6119–6123] has been extended in this paper by examining all the data in order to identify the most likely candidate for the redox-active ligand (RAL), suggested to operate between the water oxidizing complex (WOC) and Z, the electron donor to the reaction center P680. We have concluded that a very suitable candidate for RAL is the imidazole moiety of a histidine residue. The electrochemical data available on imidazole derivatives play heavily in this identification of RAL. Thus, we suggest that histidine might play the role of an electron mediator between the WOC and Z. A model of S-states in terms of their plausible chemical identity is presented here.Abbreviations J electronic spin of ion - P680 reaction center chlorophyll - RAL Redox active ligand - Sn state of the oxygen-evolving system - WOC water oxidation complex - Z electron donor to P680 Dedicated to Prof. L.N.M. Duysens on the occasion of his retirement  相似文献   
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