Heterogeneity in photosystem I. Evidence from cation-induced decrease in Photosystem I electron transport

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⁺.     

Positive cooperativity in the adherence between elementary bodies of Chlamydia trachomatis strain UW-31 and HeLa cells

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.     

Depression of mitogen response in spleen cells from reticuloendotheliosis virus-infected chickens and their suppressive effect on normal lymphocyte response

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.     

Effect of some nitrogenous salts on nitrogen transfer and protease activity in germinatingZea mays L. seeds

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.     

Characterization of the interaction of reticuloendotheliosis virus with the avian lymphoid system.

Splenic lymphocytes from chickens infected with reticuloendotheliosis virus (REV) are cytostatically impaired in their ability to undergo mitogen-induced blastogenesis ([³H]TdR uptake and proliferation), but are fully capable of eliciting cytotoxic reactions against allogeneic, ⁵¹Chromium-labeled chicken erythrocytes. Spleen cells from birds with reticuloendotheliosis (RE_s) are able to suppress DNA synthesis of normal splenic lymphocytes (N_s), but are unable to inhibit ¹[³H]TdR uptake by chick embryo fibroblasts. The suppression of the N_s mitogenic response is not restricted by major histocompatibility (B-locus) differences between populations of RE_s suppressor and N_s target cells. Moreover, infection of birds with an attenuated form of REV, which replicates in the host but does not cause tumorigenesis, also leads to suppression of phytohemagglutinin-induced, [³H]TdR uptake by host lymphocytes. These results are discussed in terms of the interaction between viral-infected/transformed cells and host defense mechanisms.     

Apparent dispensability of the carbohydrate moiety of human interferon for antiviral activity.

Human leukocyte and tritium-labeled fibroblast interferons, prepared by induction with Sendai virus and with double-stranded polyinosinic acid.polycytidylic acid respectively, have been studied in relation to the carbohydrate moieties attached to them. These interferons were partially purified by immunoabsorbance and by gel filtration. On treatment with glycosidases, about 80% of the 3H-labeled sugar moieties in this glycoprotein-containing fraction was removed without detectable alteration of the antiviral activity or antibody-binding properties characteristic of interferon. The molecular weight of leukocyte interferon was reduced by about 4000. As others have reported, the heterogeneous character of interferon revealed by isoelectric focusing was greatly reduced by the enzyme treatment.