1. Oat chloroplasts, in the presence of 0.02 M methylamine, reduce 2,6 dichlorophenolindophenol (DCIP) at a rate of 350–500 μmoles/mg chl per h, in saturating light. Brief sonication for approx. 1 min lowers the rate to approx. 50 μmoles/mg chl per h; longer sonication does not reduce activity further. During brief sonication, plastocyanin is lost from the chloroplasts. When plastocyanin is added back to sonicated fragments, DCIP reduction is approximately doubled to 100 μmoles/mg chl per h.
2. When oxidized plastocyanin is added, a transient is observed when light is first turned on: this is due to a reduction of the plastocyanin before DCIP reduction begins. When reduced plastocyanin is added, a different transient occurs: this is due to a fast photoreduction of DCIP by the plastocyanin and is followed by the slower steady state reduction of DCIP by water. When light is turned off before complete reduction of DCIP, a transient reduction of oxidized plastocyanin by reduced DCIP is seen. Insensitivity of these transients to 3(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and the greater effectiveness of 710 nm light, along with the known capacity of plastocyanin to mediate electron transfer to System I, prove that an intrinsically fast reduction of DCIP occurs at a site close to the primary photoreduced product of System I.
3. After brief sonication and washing, no residual plastocyanin was detected in chloroplast fragments, and the rate of the slow DCIP reduction (about 50μmoles/mg chl per h) sustained by such fragments was essentially identical to that maintained by fragments of mutants lacking System I activity. Following
et al.9, the simplest explanation for this slow DCIP reduction is that is occurs at a site close to System II and the system I is not involved.
4. A very slow transient reduction of DCIP occurs after extinguishing light; this presumably involves another reduction site close to System II, as suggested by
9. 相似文献
Chicken brain Arylsulfatase A (E.C.3.1.6.1) was immobilized by interaction with Concanavalin A. The immobilized enzyme retained its catalytic activity and this enzyme can be reused without appreciable loss of activity. The storage stability of bound and soluble enzymes was comparable and binding of enzyme to Concanavalin A increases its thermal stability. Kinetic studies indicated that bound enzyme shows similar anomalous kinetics as that of free enzyme but slight change was observed in relation to pH optima, Km value and activation energy. 相似文献
The antigens on the surface of human cytomegalovirus (HCMV)-infected fibroblasts which are recognized by human HCMV antibody-positive sera were characterized. Three HCMV-induced polypeptides, with apparent molecular masses of 53 to 63, 94, and 94 to 120 kilodaltons, were precipitated from 125I-surface-labeled cell extracts with different sera obtained from healthy individuals. Renal transplant recipients who were suffering from active HCMV infections recognized the same set of antigens. By the use of monoclonal antibodies, these antigens were identified as polypeptides belonging to the gcI and gcIII families of HCMV glycoproteins. 相似文献
At all stages of male gametogenesis, generative and vegetative pollen nuclei of Nicotiana sylvestris can be distinguished without ambiguity after Feulgen or ethidium bromide staining. They differ by their morphology and their apparent DNA content, always lower in vegetative nuclei. These differences provide a basis for their separation by sedimentation and fluorometry. After elimination of the another somatic cells and after crushing the pollen, vegetative and generative nuclei are separated by two successive Percoll gradients (purity 80–90%). Analysis of the gradient fractions and final purification can be done with a cell sorter. DNAs of both types are isolated by a cetyltrimethylammonium method, followed by a RNase treatment. Yields are lower for vegetative than for generative nuclei, and decrease with the age of pollen. Molecular weights and digestibility by restriction enzymes are compatible with molecular analyses. 相似文献
Summary The progeny of Dichomitus squalens CBS-432-34 is heterogeneous with respect to specific growth rate on glucose, cellulolytic ([U14C]cellulose 14CO2) and ligninolytic ([14C]synthetic lignin 14CO2) activities with little correlation between these metric characters. Variations do not show clear-cut phenotypes but rather a continuous range between extreme values pointing to multigenic control of these characters. Most homocaryons showed decreased cellulolytic or ligninolytic activity compared to the parent dicaryon. However a few homocaryons were comparable or even superior to the parent dicaryon for ligninolytic or cellulolytic activity with no correlation between each factor. Strains with reduced cellulolytic activity and altered isozyme patterns of endoglucanases were isolated in the progeny of D. squalens CBS-432-34. While the parent strain produced three main endoglucanase multiple enzymes designated EnI, EnII and EnIII, several strains in the progeny produced a different multiple enzyme pattern. In contrast to the quantitative ability to degrade cellulose, multiple enzyme pattern variation in the progeny did not show continuous variations. characterization of heterocaryon phenotypes derived from Ien+ and Ien 1 homocaryons and first filial generation (f1) analysis showed that genetic control of the multiple enzyme pattern (Ien 1 phenotype) in D. squalens is complex.
Offprint requests to: E. Odier 相似文献
EBNA-5 is one of the Epstein-Barr virus (EBV)-encoded nuclear proteins required for immortalization of human B lymphocytes. In the nuclei of EBV-transformed lymphoblastoid cell lines EBNA-5 is preferentially targetted to distinct nuclear foci. Previously we have shown (W.Q. Jiang, L. Szekely, V. Wendel-Hansen, N. Ringertz, G. Klein, and A. Rosen, Exp. Cell Res. 197:314-318, 1991) that the same foci also contained the retinoblastoma (Rb) protein. Using a similar double immunofluorescence technique, we now show that these foci colocalize with nuclear bodies positive for PML, the promyelocytic leukemia-associated protein. Artificial spreading of the chromatin by exposure to the forces of fluid surface tension disrupts this colocalization gradually, suggesting that the bodies consist of at least two subcomponents. Heat shock or metabolic stress induced by high cell density leads to the release of EBNA-5 from the PML-positive nuclear bodies and induces it to translocate to the nucleoli. In addition to their presence in nuclear bodies, both proteins are occasionally present in nuclear aggregates and doughnut-like structures in which PML is concentrated in an outer shell. Nuclear bodies with prominent PML staining are seen in resting B lymphocytes. This staining pattern does not change upon EBV infection. In freshly infected cells EBNA-5 antigens are first distributed throughout the nucleoplasm. After a few days intensely staining foci develop. These foci coincide with PML-positive nuclear bodies. At a later stage and in established lymphoblastoid cell lines EBNA-5 is almost exclusively present in the PML-positive nuclear foci. The colocalization is restricted to EBV-infected human lymphoblasts. The data presented indicate that the distinct EBNA-5 foci are not newly formed structures but the result of translocation of the viral protein to a specialized domain present already in the nuclei of uninfected cells. 相似文献
The thiol activation and aromatization of bicyclo[7.1.0]enediynes was found to be dependent of the nature of the propargyl substituent. These effects are correlated to antitumor activity. 相似文献
A brief discussion of the theoretical basis for effects of temperature on stereoselectivity of enzyme catalysed reactions is presented. In theory, the stereoselectivity of an enzymatic reaction can either increase or decrease as the reaction temperature is raised. The secondary alcohol dehydrogenase from Thermoanaerobacter ethanolicus reduces 2-butanone to (R)-2-butanol at 37° C, with increased stereoselectivity at higher temperatures and in the presence of NADP analogues. In contrast, at 37°, 2-pentanone and 2-hexanone are reduced to (S)-2-pentanol and (S)-2-hexanol, respectively, but the stereoselectivity decreases at higher temperatures and in the presence of NADP analogues. Reduction of racemic 2-methylbutanal by the primary alcohol dehydrogenase from T. ethanolicus gives (S)-2-methyl-1-butanol with greater stereospecificity at 35° (51% e.e.) than at 15° (14% e.e.). Horse liver alcohol dehydrogenase shows a preference for oxidation of the (S)-enantiomers of acyclic secondary alcohols at 25°, with a decrease in stereospecificity at higher temperatures. 相似文献