Interactions of nucleic acids with distamycins. The drug monomeric chromophore

A study of the monomeric chromophore of the oligopeptides netropsin (1), distamycin III (2), and distamycin V (3) by polarization spectroscopy techniques and molecular orbital calculations is reported. Linear dichroism spectra of the monomeric model compounds 1-methyl-2(ethylcarbamoyl)-4-acetamido-pyrrole (4) and 1-methyl-2(ethylcarbamoyl)-pyrrole (5) dissolved and oriented in lyotropic and thermotropic liquid crystals provide, together with the magnetic CD spectra, experimental checks of the theoretical calculations. The polarization directions of the investigated transition obtained by these means in this study allow us to build up in the following paper the exciton states of (1)-(3) and these provide a stereochemical interpretation of the flow linear dichroism spectra of the complexes of DNA with (2) and (3).     

Spinal ascending projections to the nucleus tractus spinalis nervi trigemini of the dog

Seven dogs were subjected 30 min to ligation of the thoracic aorta and were then kept alive 6-7 days after the ligature had been removed. Their spinal cord and brain stem were treated by the Nauta-Gygax method and the extent and appearance of preterminal and terminal degeneration of certain ascending spinal systems were analysed. In the medulla oblongata region, marked degenerating fibres from the lower thoracic and lumbosacral cord segments were found in the nucleus tractus spinalis nervi trigemini. Preterminal and terminal degenerating fibres were visualized in the caudal part of the trigeminal nuclear complex. Comparison with the literature showed these to be previously unknown projections with a relationship to the nucleus tractus spinalis nervi trigemini.     

Production ofd-mannitol fromd-aldopentoses by the yeastRhodotorula minuta

Rhodotorula minuta produced 16% ofd-mannitol and 3% ofd-arabinitol when cultivated ond-ribose, 4% of mannitol and 11% of arabinitol when grown ond-xylose, 5% ofd-mannitol and 5% ofd-arabinitol when grown ond-arabinose, and 5% ofd-mannitol and 6% ofd-arabinitol when cultivated ond-lyxose.     

Conversion of disaccharides to 3-ketodisaccharides by nongrowing and immobilized cells ofAgrobacterium tumefaciens

High-performance liquid chromatography was used to estimate 3-ketolactose and 3-ketosucrose in cultures of agrobacteria. The activities of enzymes that convert the disaccharide substrate were evaluated during batch cultivation ofAgrobacterium tumefaciens on sucrose, maltose, and lactose. The highest activity of glucoside 3-dehydrogenase and a slight activity of disaccharide-hydrolyzing enzymes were found in cells grown on lactose. Nongrowing cells converted lactose to 3-ketolactose faster than immobilized cells did. Immobilization of cells into polysaccharide gels did not stabilize the activity of glucoside 3-dehydrogenase. Glutaraldehyde cross-linking of the cell content led to an inactivation of the respiratory chain but Fe³⁺ could be used as an electron acceptor. Cells treated with glutaraldehyde converted lactose faster than nongrowing ones but the activity of glucoside 3-dehydrogenase was not stable.     

Relationship between a 47-kDa cytoplasmic membrane polypeptide and nitrate transport in Anacystis nidulans

The polypeptide composition of cytoplasmic membranes of the cyanobacterium Anacystis nidulans changes in response to variations in the nitrogen source available to the cells, differing specifically in the amount of a polypeptide of 47-kDa molecular mass. Synthesis of the polypeptide and expression of nitrate transport activity are repressed by ammonium. Transfer of ammonium-grown cells to a medium containing nitrate as the sole nitrogen source results in parallel development of the 47-kDa polypeptide and nitrate transport activity of the cells. These results suggest the involvement of the 47-kDa cytoplasmic membrane polypeptide in nitrate transport by A. nidulans.     

Forming sparse representations by local anti-Hebbian learning

How does the brain form a useful representation of its environment? It is shown here that a layer of simple Hebbian units connected by modifiable anti-Hebbian feed-back connections can learn to code a set of patterns in such a way that statistical dependency between the elements of the representation is reduced, while information is preserved. The resulting code is sparse, which is favourable if it is to be used as input to a subsequent supervised associative layer. The operation of the network is demonstrated on two simple problems.     

Variable conservation of nucleolus organizer regions during karyotypic evolution in Microtidae

The location of the nucleolus organizer regions (NORs) was studied in four species of Microtidae (Microtus nivalis, M. cabrerae, M. arvalis, and Arvicola sapidus). The comparative study of these locations shows that some NORs have been conserved despite the chromosome rearrangements that have occurred through karyotypic evolution, while others have been lost. In addition, there are many chromosomes in which NORs seem to have appeared or been lost without apparent relation to the chromosome rearrangements. Some hypotheses regarding these facts are discussed in the text.     

Prothymosin alpha expression is associated to cell division in rat testis

Summary Using immunohistochemical methods, we have investigated the cellular distribution of prothymosin alpha (ProT) in adult rat testis. A policlonal antibody raised against thymosin alpha 1 conjugated to keyhole limpet hemocyanin was used. ProT immunoreactivity was observed in the cytoplasm and nucleus of spermatogonia and primary spermatocytes in initial phases of the first meiotic division, preleptotene, leptotene and zygotene. However, in pachytene phase they already showed a weak or negative staining. On the other hand, secondary spermatocytes, spermatids, spermatozoa and Sertoli cells were not stained. Based on this fact we suggest that ProT is present in the proliferative cycle in the final steps of G₁ phase, throughout the S and G₂ phases and in initial steps of the prophase.