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Biomedical subjects

B Ivanov

Publications and source records attributed to B Ivanov.

At least 19 recordsLinked to original sources
PubMed2000

Influence of ascorbate and the Mehler peroxidase reaction on non-photochemical quenching of chlorophyll fluorescence in maize mesophyll chloroplasts.

Non-photochemical quenching of chlorophyll fluorescence (NPQ) and quantum yield of photosystem II (PSII) were studied with intact mesophyll chloroplasts of maize (Zea mays L.) during the initial minutes of illumination using the pulse-modulated chlorophyll fluorescence technique. Non-photochemical quenching was rapidly reversible in the dark at any point during illumination, which is indicative of energy-dependent dissipation of energy (mediated via thylakoid delta pH changes and ascorbate-dependent synthesis of zeaxanthin). In chloroplasts suspensions including 15 mM ascorbate in the medium, with addition of oxaloacetate and pyruvate, the PSII yield, rate of reduction of oxaloacetate and phosphorylation of pyruvate reached a maximum after approximately 2 min of illumination. Under these conditions, which promote phosphorylation and a decreased delta pH across the thylakoid membrane, NPQ rose to a maximum after 2-3 min of illumination, dropped to a minimum after about 6 min, and then increased to a steady-state level. A rather similar pattern was observed when leaves were illuminated following a 30-min dark period. Providing chloroplasts with higher levels of ascorbate (60 mM), prevented the transient drop in NPQ. Anaerobic conditions or addition of potassium cyanide caused a decrease in PSII yield, providing evidence for operation of the ascorbate-dependent Mehler-peroxidase reaction. These conditions also strongly suppressed the transient drop in NPQ. Dithiothreitol, an inhibitor of violaxanthin de-epoxidase, caused a large drop in NPQ even in the presence of high levels of ascorbate. The results suggest that the decline of NPQ occurs in response to an increase in lumen pH after initiation of phosphorylation, that this decline can be suppressed by conditions where ascorbate is not limiting for violaxanthin de-epoxidase, and that the increase of NPQ after such a decline is the result of development of energy dissipation in PSII reaction centers.

Anaerobiosis↗
PubMed2000

The competition between methyl viologen and monodehydroascorbate radical as electron acceptors in spinach thylakoids and intact chloroplasts.

In spinach thylakoids prepared from intact chloroplasts by shocking in the presence of ascorbate to preserve the operation of ascorbate peroxidase, the rate of oxygen uptake with methyl viologen as acceptor decreased in response to the addition of H2O2. Such a decrease was not observed in the presence of KCN or when the thylakoids lost ascorbate peroxidase activity. Illumination of intact chloroplasts in the presence of H2O2 and methyl viologen showed an initial rate of oxygen exchange, which is intermediate between the initial rate of oxygen evolution in the presence of H2O2 alone and steady-state oxygen uptake in the presence of methyl viologen. The data showed that monodehydroascorbate radical generated in ascorbate peroxidase reaction could compete with methyl viologen for electrons supplied by the electron transport chain in both thylakoids and intact chloroplasts. During the illumination of intact chloroplasts the rate of oxygen uptake increased. The presence of nigericin swiftly led to steady-state oxygen uptake, and to a clear-cut 1:1 relationship between the electron transport rate estimated from fluorescence assay and the electron transport rate determined from oxygen uptake, taking the stoichiometry 1 O2:4 e. The increase in oxygen uptake was attributed to the cessation of monodehydroascorbate radical generation brought about by consumption of intrachloroplast ascorbate in the peroxidase reactions, and the effects of nigericin were explained by acceleration of such consumption. The competition between methyl viologen and monodehydroascorbate radical in the intact chloroplasts was estimated under various conditions.

Ascorbate Peroxidases↗
PubMed1998

Synthetic integrin-binding peptides promote adhesion and proliferation of human periodontal ligament cells in vitro.

Periodontal ligament (PDL) cells have been shown to express several integrins (alphav, alpha5, beta1, beta3) that use RGD (arginine-glycine-aspartic Acid)-dependent mechanisms for the recognition and binding of their ligands. The objective of this study was to evaluate the effects of certain integrin-binding cyclic and linear synthetic RGD-containing peptides on PDL cells' adhesion, proliferation, and de novo protein synthesis in vitro. Fifth passages of normal human PDL cells established from teeth extracted from patients (ages 12 to 14) for orthodontic reasons were used for all experiments. Synthetic peptides containing the EPRGDNYR sequence in two different spatial conformations (linear and cyclic) were covalently attached to bovine serum albumin (BSA). Type I collagen, EPRGDNYR-BSA conjugates, 1:1 mixtures of type I collagen and conjugates, as well as BSA (a negative control) were coated on bacteriological plastic and evaluated for their attachment-promoting activities. In addition, the effects of these substrates on cell proliferation were evaluated by [3H]thymidine incorporation by the PDL cells. For attachment and spreading, the cyclic forms of EPRGDNYR-BSA conjugate and type I collagen were most potent, followed by linear EPRGDNYR-BSA conjugate. The effects of all collagen/conjugate mixtures were equivalent to that of type I collagen except for the collagen/linear EPRGDNYR-BSA mixture, which was less potent. The cyclic EPRGDNYR-BSA conjugate was the most effective substrate to stimulate cell proliferation, and it was followed in potency by the linear peptide-BSA conjugate. Collagen alone did not stimulate [3H]thymidine incorporation above the control level. Mixtures of collagen with all of the conjugates showed stimulatory effects similar to that of the cyclic peptide-BSA conjugate. No significant differences in de novo protein synthesis were detected. These results suggest that the synthetic RGD-containing peptides attached to a carrier are potent ligands for the human PDL cells, and that they could provide a basis for the development of new strategies aimed at the regeneration of the periodontium.

Adolescent↗
PubMed1996

A synthetic conformational epitope from the C4 domain of HIV Gp120 that binds CD4.

The fourth conserved domain of the human immunodeficiency virus type 1 (HIV-1) envelope, the C4 region of glycoprotein 120 (gp120), is believed to be a major part of gp120 that is necessary for binding to CD4. Recently, we found that C4 in gp120 is probably an alpha-helix, because antibodies made against helical constructs of C4 react with native and recombinant gp120 but antibodies against linear C4 constructs do not. For the present study, we performed experiments to determine, first, if CD4 could bind to the helical C4 constructs and, second, if the binding was comparable with CD4 binding to gp120. Immobilized helical constructs derived from the C4s from HIV-1 and HIV-2 bound biotinylated recombinant CD4 with Kd values of 8.59 nM and 14.59 nM, respectively. Recombinant soluble CD4 inhibited the binding of biotinylated CD4 to the C4 construct from HIV-1 with a Kd of 9.88 nM, and recombinant gp120 blocked the binding of CD4 to the immobilized helical construct from C4 of HIV-1 with a Kd of 8.08 nM. The C4 peptide-(419-436) from HIV-1 (KIKQIINMWQEVGKAMYA-NH2) blocked CD4 binding to gp120 but only in a buffer containing 0.03% Brij 35 where the peptide displayed 17 +/- 1% alpha-helix; without the Brij 35, peptide-(419-436) displayed no helical content. The Kd for the peptide-(419-436) blocking CD4 binding to gp120 in Brij 35-containing buffer was found to be 42 microM. These results indicate that C4 constructs from HIV-1 and HIV-2 do bind CD4, but the constructs must display an alpha-helical conformation to do so. In addition, the results reported here will provide answers to key questions about structural requirements for HIV vaccines and therapeutics that hinge on understanding the molecular nature of the gp120-CD4 interaction as the first step in the HIV infection process.

Amino Acid Sequence↗
PubMed1996

Bone sialoprotein peptides are potent inhibitors of breast cancer cell adhesion to bone.

Bone and bone marrow are important sites of metastasis formation in breast cancer. Extracellular matrix proteins with attachment properties are generally believed to play a key role in tumorigenesis and metastasis formation. We have investigated whether mammary carcinoma cells (MDA-MB-231) can recognize constructs of the fairly bone-specific human bone sialoprotein, which encompass the RGD sequence (EPRGD-NYR). Exogenously added bone sialoprotein peptides with this amino acid sequence in their backbone structure, but not the more common fibronectin-derived GRGDS peptide, strongly inhibited breast cancer cell adhesion to extracellular bone matrix at micromolar concentrations. Most cyclic derivatives with the EPRGDNYR sequence were more effective inhibitors of tumor cell adhesion to bone than their linear equivalents. Furthermore, changes in the RGD-tripeptide of the backbone structure of the constructs, removal of the NYR flanking sequence, or a different tertiary cyclic structure significantly decreased their inhibitory potencies. In addition, the RGE-analogue EPRGENYR was capable of inhibiting breast cancer cell adhesion to bone, albeit to a lesser extent. We conclude therefore, that the inhibitory potency of the bone sialoprotein-derived peptides on breast cancer cell adhesion to bone is not solely due to a properly positioned RGD-motif alone but is also determined by its flanking regions, together with the tertiary structure of the EPRGDNYR peptide. Synthetic cyclic constructs with the EPRGDNYR sequence may, therefore, be potentially useful as antiadhesive agents for cancer cells to bone in vivo.

Amino Acid Sequence↗
PubMed1990

[Changes in the level of immunoglobulins and other serum proteins in hepatic echinococcosis].

The humoral immunity and the protein-synthesizing function of the liver of 35 patients with liver echinococcosis were studied. No humoral immunity deficit was found. Statistically significant abnormalities in a number of proteins were reduced, with evidence of reduced protein-synthesizing liver function. Inferences are made on the anesthesia, resuscitation and operative interventions, in connection with the results of the study.

Adolescent↗
PubMed1982

[Immunoglobulin concentrations and their correlation with the level of antibodies in echinococcosis patients].

A comparison of immunoglobulin concentrations between 136 patients with surgically proved echinococcosis and control persons revealed significantly higher concentrations of immunoglobulins only in the IgG class, a phenomenon, which was more pronounced in patients with secondary echinococcosis. In the first twelve months after surgical treatment the IgG and IgA values decreased faster than the IgM values, however, in the postoperative period the IgG persisted longer than the other immunoglobulins. Antibody titers and IgG concentrations observed showed a positive correlation in the follow-up time. From these results it is suggested, that the antibodies before and after surgical treatment of echinococcosis belong to the IgG class.

Antibodies↗
PubMed1981

[Case of light-chain plasmacytic leukemia].

A female patient aged 60, is described, with plasmacellular leukemia, with disturbance in the light chains of immunoglobulins--light chain plasmacellular leukemia. The clinical picture combines the signs of blast leucosis with those of the light chain disease. The disease had an acute course, failing to respond to the treatment, with a lethal end, about 40 days after the manifestation of the clinical symptoms, better resembling blast leucosis than myeloma.

Female↗
PubMed1980

[Repair of chromosomal aberrations in a human peripheral blood lymphocyte system after single and split-dose x-irradiation].

Whole human peripheral blood was exposed either acutely to 125 or 250 R X-rays or in fractions to 125+125 R X-rays at varying cell cycle times, namely, 0, 2, 4, 6, 8, 12, 16, 24, 30, 40 or 45 hours after culture initiation. Well spread metaphase chromosomes were examined for the following types of structural chromosome aberrations: dicentrics, rings, interstitial deletions, symetrical translocations, chromatid and chromosome fragments. Most noteworthy were found to be the polycentric + ring data. With acute radiation given at any of the times over the presynthetic period, the yields of these aberrations were consistently within the range of 17-20% for the 125 R dose and 66-73% for 250 R. For either acute dose given at later times, the aberration yields decreased to fall to 1% by the end of the synthetic period. With fractionated 125+125 R exposures the following rates were obtained: irradiation at 2 hr time in culture, 44.15%; 4 hr, 50.82%; 6 hr, 55.16%; 8 hr, 58,32% (peak rate): 12 hr, 55.48%. The downward trend persisted to the end of the presynthetic period and during the synthetic period. Statistical data treatment indicated acute and fractionated exposures to differ significantly in production of polycentric+ring yields, as well as in those of other aberration types and total breakage per cell. It may be concluded from our findings that the time course of repair processes is of an undulated pattern, with peak intensity within the first hours of the presynthetic period, a fall by 8 hr and a following renewed rise; repair was found to occur nearly to the end of the synthetic period.

Cell Cycle↗
PubMed1980

[Chromosome aberrations in human peripheral blood lymphocytes after single and split-dose x-irradiation].

Effects of single exposures to 125 or 250 R and those of fractionated irradiations of 2.125 R on human lymphocytes were studied upon the chromosome aberration yields in blood maintained in a refrigerator at 5 degrees C for the intervals between the irradiations. Single irradiations succeeded venepuncture; the same holds for the first dose from the fractionated one, while he second was delivered at one of the following intervals: 2.8 or 24 hours. Immediately after completion of irradiation, blood was cultured to obtain metaphase slides for cytogenetic analysis. No repair processes were observed in the hereditary cell structures of fractionatedly irradiated blood if it was maintained at 5 degrees C for the intervals between irradiations. More chromosomes fragments, interstitial deletions, aberrant cells, and breakage of cells were scored, on the opposite, in fractionatedly irradiated blood, which was stored for 24 hours. These were even with high statistically significant differences when compared with singly exposed cells to the same doses. This effect was likely to be due to blood stirage.

Chromosome Aberrations↗
PubMed1979

[Cytogenetic and hormonal studies of persons occupationally irradiated with ionizing radiation].

Cytogenetic investigations were carried out on 23 subjects and hormonal -- on 18 of them, working in the sphere of ionizing radiation at medical institutions. After the quantitative processing of the results from the cytogenetic investigations, statistically significant differences were established to exist in cell obtaining with aberations, chromozome and chromatide fragments as compared with the spontaneous frequency of healthy subjects. Statistically significant differences were observed also in the group with length of service over 10 years as regards the dicentrics obtaining as well. With the follow-up of hormone concentrations in blood plasma a statistical decrease was found in the level of sex hormones -- testosterone in males and progesterone in females, accompanied by increased level of FSH, suggesting a primarily damage of gonads (testis and ovaries). Plasma cortisol level is statistically significant increased in all subjects examined whereas aldosterone level is normal in subjects with a length of service to 10 years and statistically significant decrease with a length of service over 10 years.

Adult↗