The inner-mitochondrial distribution of Oxa1 depends on the growth conditions and on the availability of substrates

The Oxa1 protein is a well-conserved integral protein of the inner membrane of mitochondria. It mediates the insertion of both mitochondrial- and nuclear-encoded proteins from the matrix into the inner membrane. We investigated the distribution of budding yeast Oxa1 between the two subdomains of the contiguous inner membrane--the cristae membrane (CM) and the inner boundary membrane (IBM)--under different physiological conditions. We found that under fermentable growth conditions, Oxa1 is enriched in the IBM, whereas under nonfermentable (respiratory) growth conditions, it is predominantly localized in the CM. The enrichment of Oxa1 in the CM requires mitochondrial translation; similarly, deletion of the ribosome-binding domain of Oxa1 prevents an enrichment of Oxa1 in the CM. The predominant localization in the IBM under fermentable growth conditions is prevented by inhibiting mitochondrial protein import. Furthermore, overexpression of the nuclear-encoded Oxa1 substrate Mdl1 shifts the distribution of Oxa1 toward the IBM. Apparently, the availability of nuclear- and mitochondrial-encoded substrates influences the inner-membrane distribution of Oxa1. Our findings show that the distribution of Oxa1 within the inner membrane is dynamic and adapts to different physiological needs.     

Das Vogelleben in Flur und Wald des deutsch-b?hmischen Mittelgebirges

Ohne Zusammenfassung     

Concanavalin A induced changes of lymphocyte p-nitrophenylphosphatase (author's transl)]

The effect of K+, Na+, Mg2+ and ATP on the p-nitrophenylphosphatase activity was investigated. As an enzyme preparation a microsomal fraction of sheep lymphocytes was used. Low concentrations of Mg2+, K+ and Na+ increased, whereas high concentrations decreased the enzyme activity. There was an inhibition of activity by ATP without Na+ in the incubation medium and an increase of enzyme activity at low K:Na-ratio. By concanavalin A in a concentration of 15 mug/ml the p-nitrophenylphosphatase activity was increased in intact cells and the microsomal fraction for 30-40%. The activation was not Na+, K+, Mg2+, p-nitrophenylphosphate or ATP dependent.     

Temperature-dependence of the proliferation of mouse bone marrow cells cultured in H2O- and D2O-media.

In an attempto to optimize and standardize the in vitro culture conditions of mouse bone marrow cells for assaying growth regulating factors, we studied the effects of incubation at low temperatures and of a nutrient medium containing deuteriumoxide instead of water. It was found that (1) the proliferative capacity of the cells is significantly increased by pre-incubation for 1-2 h at 0 degrees C rather than at 37 degrees C, measured by both a colony-forming and a 3H-thymidine (3H-tdr) uptake assay. A similar temperature effect on the colony-forming and 3H-tdr uptake ability is apparent after pre-incubation in D2O-medium, yet significantly lower than in H2O-medium. It was concluded that the previously observed protective effects of D2O on ascites tumor cell proliferation and viability and for hemolysis of human erythrocytes is not apparent in proliferating and colony-forming mouse bone marrow cells in vitro.     

Histological events leading to somatic embryo formation in cultured petioles of alfalfa

Summary An optimum 10-day exposure of petioles of alfalfa [Medicago sativa ssp.falcata (L.) Arcangeli] to 2,4-dichlorophenoxyacetic acid or 2,4,5-trichlorophenoxyacetic acid results in the semisynchronous production of somatic embryos starting about 4 days after transfer to a non-auxin-containing medium. The timing of cell division induction in the petiole explants was found to vary depending on the petiole tissue type. Cells adjacent to the vascular bundles divide first at about 48 h after exposure to auxin, closely followed by those of the inner parenchyma, whereas most of the cells of the subepidermal and epidermal layers start to divide later, between 72 and 120 h. Two different sources of callus were also evident. Cells adjacent to the vascular bundles and the inner parenchyma cells were the primary source of callus when a short, 2-day (non-embryo-producing) exposure to auxin was used. In contrast, the subepidermal and epidermal cells were the primary source of callus tissue when a longer, 10-day (embryo producing) exposure was used. It is concluded that the source of somatic embryos is primarily the daughter cells of the subepidermal or epidermal tissue or both.