Simultaneous effect of organic modifier and physicochemical parameters of barbiturates on their retention on a narrow-bore PGC column

The retention time of 22 barbituric acid derivatives was measured on a narrow-bore porous graphitized carbon (PGC) column using water-dioxane mixtures as mobile phases. The capacity factor (k), theoretical plate number (N), and asymmetry factor (AF) were calculated for each solute in each mobile phase. The relationships between chromatographic characteristics and physicochemical parameters of solutes were elucidated by stepwise regression analysis (SRA). SRA indicated that the binding of barbiturates to the PGC surface is of mixed character electrostatic and apolar interactive forces are equally involved. Sterical correspondence between the surface of the stationary phase and the solutes also exert a significant influence on the retention behavior.     

Ventricular beat detection in single channel electrocardiograms

Background  

Detection of QRS complexes and other types of ventricular beats is a basic component of ECG analysis. Many algorithms have been proposed and used because of the waves' shape diversity. Detection in a single channel ECG is important for several applications, such as in defibrillators and specialized monitors.     

The fate of the arachnoid villi in humans

Villi arachnoidales undergoes in the course of life changes in relation to the skull bones and sinuses. Our aim was to determine the relations of the villi arachnoidales to the skull bone and/or sinuses from the neonatal period to adults. The investigations were performed on collection of 50 disarticulated macerated skull bones from the new-born to 30 years of age and on 20 skulls from individuals in the life period from 30 to 80 years of age. Villi arachnoidales produced imprints on the skull bones in the shape of holes and/or furrows corresponding to different shape of the villi arachnoidales. These imprints appeared very early in the period when the bony sprouts of the large skull bones received a thin covering of compact bone, the future lamina vitrea. At that time villi arachnoidales had no connection with the dural sinuses but with the diploe and with the diploic veins. By agglomeration of the villi in larger and large formations, granula meningea, Pacchionian granulations, the contact to sinuses was realized by means of short channels. The structural changes of villi arachnoidales may produce thrombophlebitis and hydrocephalus externus, especially in children. The fate and the relations of the villi arachnoidales are therefore of great importance for neurologist, neurosurgeon and otorhinolaryngologist.     

Glycation and post-translational processing of human interferon-gamma expressed in Escherichia coli

Until recently, nonenzymatic glycosylation (glycation) was thought to affect the proteins of long living eukaryotes only. However, in a recent study (Mironova, R., Niwa, T., Hayashi, H., Dimitrova, R., and Ivanov, I. (2001) Mol. Microbiol. 39, 1061-1068), we have shown that glycation takes place in Escherichia coli as well. In the present study, we demonstrate that the post-translational processing (proteolysis and covalent dimerization) observed with cysteineless recombinant human interferon-gamma (rhIFN-gamma) is tightly associated with its in vivo glycation. Our results show that, at the time of isolation, rhIFN-gamma contained early (but not advanced) glycation products. Using reverse phase high performance liquid chromatography in conjunction with fluorescence measurements, enzyme-linked immunosorbent assay, and mass spectrometry, we found that advanced glycation end products arose in rhIFN-gamma during storage. The latter were identified mainly in the Arg/Lys-rich C terminus of the protein, which was also the main target of proteolysis. Mass spectral analysis and N-terminal sequencing revealed four major (Arg140/Arg141, Phe137/Arg138, Met135/Leu136, and Lys131/Arg132) and two minor (Lys109/Ala110 and Arg90/Asp91) cleavage sites in this region. Tryptic peptide mapping indicated that the covalent dimers of rhIFN-gamma originating during storage were formed mainly by lateral cross-linking of the monomer subunits. Antiviral assay showed that proteolysis lowered the antiviral activity of rhIFN-gamma, whereas covalent dimerization completely abolished it.     

Common origin and evolution of glycosyltransferases using Dol-P-monosaccharides as donor substrate

On the basis of the analysis of 64 glycosyltransferases from 14 species we propose that several successive duplications of a common ancestral gene, followed by divergent evolution, have generated the mannosyltransferases and the glucosyltransferases involved in asparagine-linked glycosylation (ALG) and phosphatidyl-inositol glycan anchor (PIG or GPI), which use lipid-related donor and acceptor substrates. Long and short conserved peptide motifs were found in all enzymes. Conserved and identical amino acid positions were found for the alpha 2/6- and the alpha 3/4-mannosyltransferases and for the alpha 2/3-glucosyltransferases, suggesting unique ancestors for these three superfamilies. The three members of the alpha 2-mannosyltransferase family (ALG9, PIG-B, and SMP3) and the two members of the alpha 3-glucosyltransferase family (ALG6 and ALG8) shared 11 and 30 identical amino acid positions, respectively, suggesting that these enzymes have also originated by duplication and divergent evolution. This model predicts a common genetic origin for ALG and PIG enzymes using dolichyl-phospho-monosaccharide (Dol-P-monosaccharide) donors, which might be related to similar spatial orientation of the hydroxyl acceptors. On the basis of the multiple sequence analysis and the prediction of transmembrane topology we propose that the endoplasmic reticulum glycosyltransferases using Dol-P-monosaccharides as donor substrate have a multispan transmembrane topology with a first large luminal conserved loop containing the long motif and a small cytosolic conserved loop containing the short motif, different from the classical type II glycosyltransferases, which are anchored in the Golgi by a single transmembrane domain.     

Role of structure and pH in cyclization of allene oxide fatty acids: implications for the reaction mechanism

Incubations of allene oxide synthases of flax or maize with the E,E-isomers of the 13- and 9-hydroperoxides of linoleic acid (E,E-13- and E,E-9-HPOD, respectively) at pH 7.5 afforded substantial yields of trans-disubstituted cyclopentenones. Under the conditions used, (Z,E)-HPODs were converted mainly into -ketols and afforded only trace amount of cyclopentenones. These findings indicated that changing the double bond geometry from Z to E dramatically increased the rate of formation of the pericyclic pentadienyl cation intermediate necessary for electrocyclization of 18:2-allene oxides and thus the yield of cyclopentenones. The well-known cyclization of the homoallylic allene oxide (12,13-EOT) derived from -linolenic acid 13-hydroperoxide (E,Z-13-HPOT) into cis-12-oxo-10,15-phytodienoic acid was suppressed at pH below neutral and was not observable at pH 4.5. In contrast, cyclization of the allene oxide ((9E)-12,13-EOD) derived from (E,E)-13-HPOD was slightly favoured at low pH. The finding that the cyclizations of 12,13-EOT and (9E)-12,13-EOD were differently affected by changes in pH suggested that the mechanisms of cyclization of these allene oxides are distinct.     

Diffusion approximation of the stochastic process of microtubule assembly

Microtubules are protein polymers that guide intracellular motility. Stochastic switching of a microtubule between states of elongation, shortening, and pause is described in detail by the dynamic instability (DI) model. Recently we have described the dynamics of microtubules phenomenologically as generalized diffusion of their ends. Genesis of the diffusion dynamics and accuracy of diffusion model are studied in this work. It is shown that wandering of the end of a microtubule undergoing DI asymptotically approaches the Wiener diffusion process. Accuracy of the diffusion approximation is evaluated by comparing its predictions with results of simulation of DI. Stationary distributions of microtubule length and lifetime that are predicted by both models differ qualitatively between two cell types considered. However, predictions of the diffusion model are in each case practically identical to predictions of the DI model being also consistent with experimental data. The peculiar stochastic process of microtubule assembly thus converges at cell scale to a kind of widespread-in-nature diffusion process. This result is considered an example of qualitative change in dynamical properties in transition from the molecular to cellular level of biological organization. Additionally, it suggests employment of diffusion process theory in studying functions of microtubules in the cell.