The secondary structure of amides of adenylic acid containing D- and L-aromatic amino acids

Adenylyl-(5'leads to N)-amino acids containing as amino components, methyl esters of D-, L- and DL-phenylalanine, D-, L- and DL-tyrosine, and D-, L- and DL-tryptophan have been investigated by proton magnetic resonance (PMR) spectroscopy and circular dichroism (CD). The temperature and pD dependences of proton chemical shifts of these compounds have been studied. These data, together with the magnitudes of the upfield chemical shifts of the PMR signals of adenine and aromatic amino acids residues in adenylyl-(5'leads to N)-amino acids, have enabled us to construct conformational models of these compounds. The proposed conformation has been substantiated by the CD results. It is shown that in adenylyl-(5'leads to N)-amino acids the planes of adenine and amino acid aromatic moieties are roughly parallel. The aromatic rings of phenylalanine and tyrosine are localized approximately above the centre of adenine. In adenylyl-(5'leads to N)-D, -(L)-tryptophan, the six-membered rings of the indole overlaps the five-membraned ring of adenine indole partially overlaps the six-membered ring of adenine. A difference in the non-covalent interactions of D- and L-amino acids with nucleotides has been revealed. The mutual localization of the aromatic systems of AMP and the amino acids and also the positions of -OCH3 group with respect to the centre of the amino acid aromatic moiety differs in the series of the studied nucleotide derivatives of D- and L-amino acids.     

The 32- and 14-kilodalton subunits of replication protein A are responsible for species-specific interactions with single-stranded DNA

Replication protein A (RPA) is a multisubunit single-stranded DNA-binding (ssDNA) protein that is required for cellular DNA metabolism. RPA homologues have been identified in all eukaryotes examined. All homologues are heterotrimeric complexes with subunits of approximately 70, approximately 32, and approximately 14 kDa. While RPA homologues are evolutionarily conserved, they are not functionally equivalent. To gain a better understanding of the functional differences between RPA homologues, we analyzed the DNA-binding parameters of RPA from human cells and the budding yeast Saccharomyces cerevisiae (hRPA and scRPA, respectively). Both yeast and human RPA bind ssDNA with high affinity and low cooperativity. However, scRPA has a larger occluded binding site (45 nucleotides versus 34 nucleotides) and a higher affinity for oligothymidine than hRPA. Mutant forms of hRPA and scRPA containing the high-affinity DNA-binding domain from the 70-kDa subunit had nearly identical DNA binding properties. In contrast, subcomplexes of the 32- and 14-kDa subunits from both yeast and human RPA had weak ssDNA binding activity. However, the binding constants for the yeast and human subcomplexes were 3 and greater than 6 orders of magnitude lower than those for the RPA heterotrimer, respectively. We conclude that differences in the activity of the 32- and 14-kDa subunits of RPA are responsible for variations in the ssDNA-binding properties of scRPA and hRPA. These data also indicate that hRPA and scRPA have different modes of binding to ssDNA, which may contribute to the functional disparities between the two proteins.     

A case of systemic lupus erythematosus in a 13-year-old girl]

The test with running on a treadbane showed a 56% increase of working capacity in the control group of male albino mice on the 20th day of training. Oral administration of elton, leveton, phytoton, and adapton, as well as Leuzea and Rhodiola extracts and Schisandra chinensis tincture caused a statistically significant increase in the time of running on the treadbane of animals by the 10th day of medication. The increase in the working capacity of the animals was more marked by the 20th day. In the test of swimming "to the limit" adapton, phytoton, leveton, and elton increased to a greater extent the working capacity of male albino rats in diminishing succession (from 213 to 168%). Schisandra tincture and Rhodiola and Leuzea extracts also increased the swimming time of the animals by 135-159%.     

The development and utilization of the case-based help-desk support system HOMER

Current case-based reasoning (CBR) process models present CBR as a low-maintenance AI-technology and do not take the processes that have to be enacted during system development and utilization into account. Since a CBR system can only be useful if it is integrated into an organizational structure and used by more than one user, processes for continuous knowledge acquisition, utilization and maintenance have to be put in place. In this paper the shortcomings of classical CBR process models are analyzed, and, based on the experiences made during the development of the case-based help-desk support system HOMER, the managerial, organizational and technical processes related to the development and utilization of CBR systems are described.     

Degradation of PLA,PLGA homo‐ and copolymers in the presence of serum albumin: a spectroscopic investigation

Poly(D,L ‐lactide‐co‐glycolide) samples with different glycolide contents, ie 85:15, 75:25 and 50:50 mole ratios of lactide to glycolide, and poly(L ‐lactide) were obtained from a commercial source. Polymer films of 15 µm thickness were prepared by a solvent‐casting method. Degradation studies were conducted at 37 °C in pH 7.4 phosphate buffered saline and in bovine serum albumin solution. The degradation behaviour of the films was followed by UV and FTIR spectrophotometry and viscometric and gravimetric measurements. Spectroscopic investigations showed that during the first month of degradation, both the chain length and the chain chemical structure changed, especially in the presence of bovine serum albumin. The short chains are attributed to the formation of new ester groups; however, the end‐groups may be aldehyde‐ or ketone‐like structures. While the intrinsic viscosities of all polymers decreased continuously after being exposed to the degradation media, insignificant mass loss occurred during the experimental investigation. © 2000 Society of Chemical Industry