Biomedical subjects

P Nikolov

Publications and source records attributed to P Nikolov.

At least 19 recordsLinked to original sources

PubMed2005

Adsorption of NO on alumina-supported oxides and oxide-hydroxides of manganese.

The adsorption capacity for NO of alumina-supported oxides and oxide-hydroxides of manganese have been studied. Two series of samples have been prepared by precipitation on gamma-alumina and appropriate thermal treatment. The samples have been characterized by adsorption methods, magnetic methods, electronic paramagnetic resonance (EPR), transient response technique, and temperature-programmed desorption (TPD). The influence of the concentration of the initial manganese-containing solution has been investigated. The sample, prepared with a solution with Mn concentration of 4 g/100 ml, has been shown to be the best adsorbent for NO under the conditions of the experiment. It has been found that the presence mainly of Mn3+ ions on the surface of the support is probably responsible for the enhanced adsorption capacity.

Adsorption↗

PubMed1998

Steady-state and time-resolved fluorescence of Esperase: comparison with the X-ray structure in the region of the two tryptophans.

Fluorescence emission properties of the alkaline protease Esperase have been investigated using steady-state and time-resolved fluorescence spectroscopy. The local polarity and solvent accessibility of the tryptophyl chromophores is characterized. Quenching studies demonstrated that Trp 6 and Trp 113 are 'buried' to acrylamide, iodide ions and caesium ions. An abnormally low tryptophan quantum yield was calculated showing that the emission of the two indole rings is significantly quenched by nearby side chains or peptide bonds. The fluorescence decay of PMS-Esperase was well fitted by two exponentials with lifetimes of 2.7 and 0.35 ns. X-ray data for Esperase (S. Klupsch, Ph.D. Thesis, University of Hamburg, Hamburg, Germany) in the region of the two tryptophans were used to explain the observed emission properties. Gln 182 and Asn 204 as well as Asn 117 and Met 119 are the most likely quenchers, respectively, of the Trp 6 and Trp 113 fluorescence. The two tryptophans in Esperase are 'buried' in hydrophobic regions and are excellent intrinsic probes to study folding-unfolding reactions. Experiments in the presence and absence of added calcium ions demonstrated the stabilizing role of the Ca(2+)-binding sites.

Computer Graphics↗

PubMed1996

Fluorescence decay of tryptophans in serine proteinases from microorganisms: relation to X-ray models.

Fluorescence decay kinetics of indole groups in five proteinases from microorganisms are reported. The data show differences between the excited state lifetimes of the tryptophans located in identical positions in the polypeptide chains of the closely related proteinases mesentericopeptidase and subtilisin Novo. The lifetime of the single Trp 113 in subtilisins DY and Carlsberg are identical. The microenvironments of this residue in the four subtilisins are identical and probably its fluorescence is quenched in these proteins. The crystallographic models of the enzymes investigated were analysed in the region of the tryptophyl residues and provide an explanation for the observed emission properties.

Bacillus↗

PubMed1994

Interaction of phthalocyanines with lipid membranes: a spectroscopic and functional study on isolated rat liver mitochondria.

Absorption and emission spectroscopic studies on Zn(II)-phthalocyanine (ZnPc) incorporated into unilamellar liposomes of dipalmitoylphosphatidylcholine, sometimes added with cholesterol or cardiolipin, and released to rat liver mitochondria via the three types of liposomal vesicles indicated that: (a) ZnPc predominantly dissolves in all lipid domains of biological membranes with the exception of cardiolipin-containing regions; a partial localization of ZnPc in protein binding sites is also postulated; (b) the spectroscopic properties of ZnPc, although mainly determined by the aggregation state of the dye, are somewhat influenced by the physico-chemical characteristics of the lipid environment; (c) ZnPc-binding lipid domains in mitochondria are mainly localized in the outer membrane; this conclusion is clearly deduced from the trends of Arrhenius plots of the ZnPc fluorescence quantum yield in whole mitochondria and isolated inner or outer membrane in the temperature range -10 degrees C-(+)45 degrees C; (d) the nature of the ZnPc-binding site in mitochondria is not dependent on the chemical composition of the liposome carrier, contrary to what observed for other hydrophobic dyes, such as porphyrins. This has been also confirmed by photosensitization experiments. Actually, illumination of ZnPc-loaded mitochondria by 600-700 nm light causes a decline of the respiratory control ratio, which is essentially dependent on the amount of incorporated photosensitizer, irrespective of the composition of the carrier.

Animals↗

PubMed1990

[The pneumodynamic barium x-ray study of small intestine adhesions (a preliminary report)].

Small-intestinal adhesions are not very rare, but on conventional X-ray examination are frequently missed because of their poor semiotics. By the method of pneumodynamic-barium X-ray examination, which allows to obtain high-quality double-contrast image, in addition to the better visualized classical symptoms--exostotic rebounds, diverticulum-like deformities, peristaltic spasms, spastic contractions etc, one may evince also the following new criteria: when inflated the intestines do not freely increase their volume, as is normal, are not unplaited along the entire abdomen, but remain amassed in a definite zone (usually in the left half); On external pressure the inflated loops do not move, as do the ones without adhesions, but remain fixed, so that their structure remains unchanged. The intestinal loops are crooked with acute angles; when in a normally inflated state, they are not crooked, but long. A frequent finding in small intestinal adhesions are the V-shaped figures in whose bottom there is barium meal over which air passes. A study of the small-intestinal cannon contraction reveals insufficiency in the hydrodynamics of the intestinal passage, marked by delayed evacuation, in spite of the strong peristalsis. This method allows a more precise elucidation than the conventional X-ray examination of the abdominal status in small-intestinal adhesions and better orientates the surgeon to choose conservative or operative treatment.

Abdominal Neoplasms↗

PubMed1988

[Radionuclear encephalo-angioscintigraphic studies in transitory disorders of brain circulation in childhood].

Fifteen cases of transient cerebral ischaemia in children have been studied. Radionuclear encephaloangioscintigraphy (RNEAS) with Tc99 DTPA in combination with CT scanning, doppler sonography of extracranial head arteries and EEG were performed in all observed cases. For some children cerebral angiography was done. RNEAS study found out: stenosis of internal carotid artery or a. cerebri media in 5 cases; AV-malformations- 3; ischaemic area- 1, aneurysma- 1; increased blood permeability of the late static scintigraphy- 3. Positive correlation was established between the angioscintigraphic and sonographic findings in the cases with stenosis of internal carotid artery; between angioscintigraphic and CT results in the cases with ischaemia; between RNEAS and angiographic data in cases with AV-malformations, aneurysm and stenosis. In conclusion RNEAS could be considered as a useful, atraumatic screening method within the complex of laboratory examinations for vascular diseases in childhood.

Carotid Artery Diseases↗

PubMed1987