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31.
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The rate of electron transfer through Photosystem I (reduced 2,6-dichlorophenol indophenol (DCIPH2 → methylviologen) in a low-salt thylakoid suspension is inhibited by Mg2+ both under light-limited and the light-saturated conditions, the magnitude of inhibition being the same. The 2,6-dichlorophenol indophenol (DCIP) concentration dependence of the light-saturated rate in the presence and in the absence of Mg2+ shows that the overall rate constant of the photoreaction is not altered by Mg2+. With N,N,N′,N′-tetramethyl-p-phenylenediamine or 2,3,5,6-tetramethylphenylenediamine as electron donor only the light-limited rate, not the light-saturated rate, is inhibited by Mg2+ and the magnitude of inhibition is the same as with DCIP as donor. The results are interpreted in terms of heterogeneous Photosystem I, consisting of two types, PS I-A and PS I-B, where PS I-A is involved in cation-regulation of excitation energy distribution and becomes unavailable for DCIPH2 → methyl viologen photoelectron transfer in the presence of Mg2+. 相似文献
33.
Abstract The adherence of purified elementary bodies of Chlamydia trachomatis strain UW-31 to monolayer cultures of HeLa 229 cells exhibited kinetic evidence of positive cooperativity. An abrupt increase in the rate of adherence occurred as chlamydial dose was increased. Only freshly isolated chlamydiae showed this behavior. In the presence of the lectin wheat germ agglutinin, the stimulated adherence showed typical Michaelis-Menten kinetics. The results suggest that chlamydiae may promote their own binding to the host-cell surface, and the lectin, when cell-bound, may provide additional chlamydiae-binding sites. 相似文献
34.
Steady-state electron flux through P700 (t 20 msec) and concomitant rate of NADP reduction have been measured under weak actinic illumination as a function of concentration of ferredoxin added to broken chloroplasts isolated from peas. At suboptimal concentrations of ferredoxin this P700 is not sufficient to account for the NADP reduction. At high concentrations ferredoxin inhibits the rate of NADP reduction without affecting the P700 flux under short wavelength illumination. Under far red illumination P700 flux is also inhibited by ferredoxin at high concentrations. Addition of 5 mM Mg++ increases the rate of NADP reduction at all concentrations of ferredoxin under both kinds of illumination, while P700 flux is inhibited under short wavelength illumination and remains unchanged under far red illumination. The results indicate that the observed (20 msec) P700 is not involved in NADP reduction. 相似文献
35.
The enzyme nitrite reductase (EC 1.6.6.4) is generally assayed in terms of disappearance of nitrite from the assay medium. We describe a technique which allowed estimation of the enzyme level in leaf tissues of Vigna mungo (L). Hepper in terms of the release of the product (NH3) of the enzyme reaction. The technique is offered as an alternative, possibly more convenient method for assay of nitrite reductase in plant tissue in vivo. 相似文献
36.
Spleen cells and peripheral blood lymphocytes from chickens infected with reticuloendotheliosis virus (REV) were depressed in their responsiveness to phytohemagglutinin (PHA). When spleen cells from uninfected chickens were co-cultured with spleen cells from chickens infected with REV at 2 weeks of age, the PHA response by the normal cells was completely suppressed. Although spleen cells from chickens infected with REV at 6 or 9 weeks of age were also suppressed in their ability to respond to PHA, they did not suppress the mitogenic response of normal cells in mixed cultures. 相似文献
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Maize seeds were allowed to germinate in the presence of different nitrogenous salts for 72 h. Changes in the ethanol soluble and insoluble nitrogen were studied in the embryo and in the endosperm. Supply of Ca(NC3)2 enhanced germination and protease activity in the endosperm resulting in greater solubilisation of protein to soluble nitrogen in the seeds. NH4NO3 and (NH4)2SO4 were less effective as compared to Ca(NO3)2. Cycloheximide inhibited germination and protease activity. Pretreatment also resulted in increase in growth, soluble and insoluble nitrogen, and nitrate reductase activity in the primary leaves. Ca(NO3)2 was more effective than NH4NO3 and (NH4)2SO4. 相似文献