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Intrinsic melanogenic inhibitors with high molecular weights have been isolated from Greene's amelanotic hamster melanoma by DEAE ion-exchange and gel filtration chromatographies. The native molecular weights of two partially purified inhibitors have been determined to be 15 kDa (β-type) and 67 kDa (γ-type), respectively, using HPLC gel filtration. Both types of inhibitors, despite their inability to directly inhibit isolated tyrosinase, have been shown to markedly inhibit melanin formation in cultured B16 cells. In contrast to the β-type inhibitor, the γ-type inhibitor can induce depigmentation in B16 cells without abolishing their internal tyrosinase activity. Further, it has been determined that both inhibitors contain various amounts of unsaturated fatty acids, C15:1, C18:1, C18:2, C18:3, C20:3, and C20:4, which exhibit depigmentary activities on cultured B16 cells. C15:1 is low in the β-type, but high in the γ-type whereas C18:3 is high in the β-type but low in the γ-type. These results suggest that the differential action of these inhibitors is most likely due to the composition of the unsaturated fatty acids. 相似文献
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Growth-chamber studies were conducted to evaluate nitrogen assimilationby three hypernodulated soybean [Glycine max (L.) Merr.] mutants(NOD13, NOD24, NOD37) and the Williamsparent. Seeds were inoculated at planting and transplanted atday 7 to nutrient solution with 1 mol m3 urea (optimizesnodule formation) or 5 mol m3 NO3 (inhibits noduleformation). At 25 d after planting, separate plants were exposedto 15NO2 or 15NO3 for 3 to 48 h to evaluate N2 fixationand NO3 assimilation. Plant growth was less for hypernodulatedmutants than for Williams with both NO3 and urea nutrition.The major portion of symbiotically fixed 15N was rapidly assimilated(30 min) into an ethanol-soluble fraction, but by 24 h aftertreatment the ethanolinsoluble fraction in each plant part wasmost strongly labelled. Distribution patterns of 15N among organswere very similar among lines for both N growth treatments aftera 24 h 15N2 fixation period; approximate distributions were40% in nodules, 12% in roots, 14% in stems, and 34% in leaves.With urea-grown plants the totalmg 15N fixed plant1 24h1 was 1·18 (Williams), 1·40 (N0D1-3),107 (NOD2-4), and 0·80 (NOD3-7). The 5 mol m-3 NO3- treatmentresulted in a 95 to 97% decrease in nodule mass and 15N2 fixationby Williams, while the three mutants retained 30 to 40% of thenodule mass and 17 to 19% of the 15N2 fixation of respectiveurea-grown controls. The hypernodulated mutants, which had restrictedroot growth, absorbed less 15NO3- than Williams, irrespectiveof prior N growthcondition. The 15N from 15NO3- was primarilyretained in the soluble fraction of all plant parts through24 h. The 15N incorporation studies confirmed that nodule developmentis less sensitive to external NO3- in mutant lines than in theWilliams parent, and provide evidence that subsequent metabolismand distribution within the plant was not different among lines.These results further confirm that the hypernodulated mutantsof Williams are similar in many respects to the hyper- or supernodulatedmutants in the Bragg background, and suggest that a common mutationalevent affectingautoregulatory control of nodulation has beentargeted. Key words: Glycine max (L.) Merr., soybean, N2fixation, nitrate assimilation, nodulation mutants, 15N isotope 相似文献
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