Structural analysis of translating ribosomes. Proton magnetic resonance method

Comparison has been made of the proton magnetic resonance (PMR) spectra of translating ribosomes in the pre-translocation and post-translocation states as well as of the complexes of translating ribosomes with elongation factors Tu (EF-Tu) or G (EF-G) in the presence of the uncleavable analogue of GTP--guanylyl-imidodiphosphate (GMP-PNP). It is shown that proteins L7/L12 within the translating ribosomes possess a high intramolecular mobility both in the pre-translocation and in the post-translocation states. The interaction of EF-G with translating ribosomes results in a decrease of the mobility of the L7/L12 proteins. The interaction of EF-Tu with translating ribosomes leads to slight changes in the PMR spectra different from the changes caused by EF-G.     

The distribution and relation to the cytoskeleton of specific prosomal proteins in the oogenesis of the clawed toad]

Using immunoblotting and immunofluorescent microscopy, we showed the presence in Xenopus laevis oocytes of two prosomal proteins (27 and 31-33 kDa) and studied their distribution during oogenesis. In the ooplasm, both proteins are detected in prosomal clusters of various size. During previtellogenesis, prosomal proteins are diffusely distributed in the nucleoplasm and form evenly distributed clusters in the cytoplasm. During oocyte growth, prosomal proteins disappear from the nucleus and form animal-vegetal and cortical gradients in the cytoplasm. In the course of oocyte maturation prosomal clusters become smaller. After artificial activation of the egg, the dorso-ventral gradient of distribution of prosomal proteins is observed. Double immunohistochemical labeling revealed morphological association between prosomal clusters and fibril-like structures of the oocyte containing actin and myosin. The latter are then replaced by diffusely distributed actin and myosin. Thus, correlation is observed between localization of the acto-myosin complex of the oocyte and that of prosomal proteins.     

Structural studies of translating ribosomes. II. Comparative sedimentation analysis of pre- and post-translocation states

Using the solid-phase translation system technique where template poly(U) is covalently coupled to Sepharose through cleavable disulfide bridges translating monoribosomes carrying a polypeptide (polyPhe) of 10 to 20 amino acids long have been isolated. Both pre-translocation state and post-translocation state ribosomes have been obtained. It has been shown that the sedimentation coefficient of the pre-translocation state ribosomes exceeds that of the post-translocation state ribosomes by a magnitude of about 1S. This difference is independent on the sedimentation rate (hydrostatic pressure) in the range of 20 000 to 40 000 rev/min and, most likely, is not a direct contribution of the increase of the particle mass at the expense of an additional tRNA in the pre-translocation state ribosomes. Together with other data, this result suggests that translating ribosomes in the pre-translocation state are more compact than post-translocation state ribosomes.     

Factors that control the differentiation of stem cells. I. The change in direction of hematopoietic stem cell differentiation under the effect of differentiating T-lymphocytes]

A mixed transplantation of bone marrow cells, and lymph nodes or thymic cells of mice CBA strain into lethally irradiated hybrid recipients (CBAXC57B1)F1 is accompanied with changes in the differentiation pattern from a mainly erythroid to a mainly granuloid way. Thymectomy of either donor of bone marrow cells or recipients, or both, destroys the stem cell differentiation in the direction of granulopoieseis. Intact syngeneic lymphocytes normalize differentiation of the stem cells, but in the presence of tissue antigens these provide for the stem cell differentiation mainly in the direction of granulopoiesis. The differentiation of stem haemopoietic cells is accomplished under the thymic and lymphocyte control. T-differentiating lymphocytes (Td) are the lymphocytes controlling the stem cell differentiation.     

Effects of moderate ammonium enrichment on three submersed macrophytes under contrasting light availability

1. Increased ammonium concentrations and decreased light availability in a water column have been reported to adversely affect submersed vegetation in eutrophic waters worldwide. 2. We studied the chronic effects of moderate enrichment (NH₄–N: 0.16–0.25 mg L^?1) on the growth and carbon and nitrogen metabolism of three macrophytes (Ceratophyllum demersum, Myriophyllum spicatum and Vallisneria natans) under contrasting light availability in a 2‐month experiment. 3. The enrichment greatly increased the contents of free amino acids and nitrogen in the shoot / leaf of the macrophytes. This indicates that was the dominant N source for the macrophytes. 4. Soluble carbohydrate contents remained relatively stable in the shoot / leaf of the macrophytes irrespective of the treatments. Under ambient light, the starch contents in the shoot / leaf of C. demersum and M. spicatum increased with enrichment, whereas V. natans did not exhibit any change. The starch contents decreased in C. demersum, increased in M. spicatum and remained unchanged in V. natans after the combined treatment of enrichment and reduced light. 5. The enrichment did not affect the growth of the three macrophytes under the ambient light. However, it did suppress the growth of C. demersum and M. spicatum under the reduced light. The results indicate that a moderate enrichment was not directly toxic to the macrophytes although it might change their viability in eutrophic lakes in terms of the carbon and nitrogen metabolism.     

Activity of ectoenzymes of the heart breaking up ATP in the period of myocardial reperfusion after ischemia

Nowadays the activity of heart ectoenzymes, breaking up ATP, are determined in the undamaged tissue to eliminate the effect to the ATP of intracellular enzymes. Our aim is to study the activity of ecto-adenosine triphosphatase in the heart damaged by ischemia. It was established that the activity of ectoenzymes, breaking up ATP, may be measured in the tissue damaged by ischemia only in case when the cellular membrane becomes impermeable for the intracellular enzymes. The activity of adenosine triphosphatase is significantly reduced during the myocardial reperfusion after ischemia and appeared as one of the criteria by which we can assume the degree of the heart reperfusion damage.