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Biomedical subjects

G Todorov

Publications and source records attributed to G Todorov.

36 records · Page 2Linked to original sources
PubMed1993

Translocation of retinoblastoma protein associated with tumor cell growth inhibition.

Immunocytochemistry revealed an association between growth inhibition and a translocation of retinoblastoma protein (pRB) to the nucleoli of U-2 osteosarcoma cells inhibited in their growth by the negative growth factor NCPI (natural cell proliferation inhibitor). Similar phenomenon was demonstrated by Western blot analysis and immunocytochemistry in U937 leukemic cells inhibited in their growth and induced to differentiate by 12-O-tetradecanoylphorbol acetate (TPA). Total nuclear extract of control U937 cells gave an intense 110 KD band, while total nuclear extract of TPA treated cells produced an intense 60 KD band and a weak 110 KD band. No bands were observed for the purified nucleoli of control cells, but the purified nucleoli of TPA treated cells produced a 60 KD band. These results suggest that in the process of cell growth inhibition and differentiation, specific proteolysis of pRB and its translocation to the nucleolus may occur.

Blotting, Western↗
PubMed1993

[Changes in electrolyte excretion in the saliva of 8th-grade students of a music school in Sofia].

The present work is part of a complex study of the health problems concerning the training of schoolchildren from the musical school--Sofia in specialty violin and piano. In order to examine the changes in the activity of the sympathetic-adrenal system for tracing the concentrations of sodium, potassium and index sodium/potassium in saliva of schoolchildren from the musical school during the general education program and also during individual training. The changes established during the experiment show the dynamics in the functional state of the sympathetic-adrenal system. We have to mention, that during the individual training an increased activity of the adrenal is observed, in connection with the emotional adjustment and emotional expenditure of schoolchildren.

Bulgaria↗
PubMed1992

Increase in protein kinase C activity is associated with human fibroblast growth inhibition.

Protein kinase C (PKC) activity and DNA synthesis were measured in human fetal bone marrow fibroblasts following treatment with tumor necrosis factor alpha (TNF alpha) (500 U/ml) or conditioned media containing natural cell proliferation inhibitor (CM-NCPI). Treatment with TNF alpha led to growth stimulation (120 +/- 7% of control in 24 h, 141 +/- 6% in 72 h). At the same time particulate PKC activity diminished, reaching 55 +/- 8% of control in 24 h and remaining at this level at 72 h. CM-NCPI treatment of the cells resulted in a decrease in DNA synthesis (by 39 +/- 6% in 2 h, by 58 +/- 5% in 24 h, and by 78 +/- 8% in 72 h). This was accompanied by a significant rise in particulate PKC activity which increased over 3-fold in 2 h, over 5-fold in 24 h, and up to 11-fold in 72 h. This 11-fold elevation was maintained after 2 week exposure of the fibroblasts to CM-NCPI. The PKC inhibitor neomycin abolished CM-NCPI induced growth inhibition, whereas PKC activator 12-O-tetradecanoylphorbol 13-acetate intensified it. These results suggest that CM-NCPI acts as PKC activator and that negative growth regulation by extracellular agents may involve stimulation of PKC activity.

Bone Marrow↗
PubMed1992

Influence of cation binding on the electro-optically determined electric moments of purple membranes.

Analysis of the electro-optically determined permanent dipole moment and electric polarizability of purple membrane fragments reveals the complex nature of the membrane electric moments. The problem to distinguish between the contribution of the membrane structural charges (charged groups of the polypeptide chain and polar lipid headgroups), bound cations and the electric double layer structure deserves particular attention not only because of its importance for electro-optics but also in respect to the relation of the membrane surface electric properties to the membrane transport function. The removal of divalent cations (Ca2+ and Mg2+) bound to purple membrane in the native state induces a cation-free species of purple membrane (deionized--blue membrane) with drastically changed spectroscopic properties and function. The present paper summarizes our study on the electric moments of blue membrane and their changes during the blue to purple transition. We intended to provide an insight into the possible regulation of this reversible transition (purple-to-blue and blue-to-purple) through changes of the asymmetric charge distribution and the importance of the asymmetric interfacial charge distribution for the proton transfer in purple membranes. The changes in the electric moments (permanent and induced dipole moments) of purple membrane fragments upon di- and trivalent cations binding to cation-depleted purple membranes were studied by electric light scattering (rotational electrokinetics) in d.c. and a.c. electric fields, and by electric pulses with reversing polarity. The results show a recovery of the membrane charge asymmetry (permanent dipole moment) though not of the induced dipole moment.

Bacteriorhodopsins↗
PubMed1982

Interfacial electric polarizability of purple membranes in solution.

An investigation of the scattered light (lambda = 632.8 nm) from purple membrane suspensions with different concentrations subjected to external AC and DC electric fields has been carried out. The electric pulses used were in the field strength range 0-3.2 X 10(4) Vm-1 and the frequency range 10 Hz-1 MHz, the pulse duration being less than or equal to 0.5 s. A concentration dependence of the relative changes in the scattered light intensity was obtained, the effect being positive on orienting the suspensions by an AC field at 1 and 10 kHz, and negative in the case of a DC field. The negative effects in the diluted samples decrease and turn positive as the strength of the field increases. The positive effects show the existence of an interfacial polarizability along the plane of the membrane, and the negative ones suggest the presence of a permanent dipole moment (p), perpendicular to the plane of the membrane. The values of gamma (induced polarizability) and p were found to be on the order of 10(-28)-10(-29) Fm2 and 10(-24) Cm, respectively. An explanation in terms of membrane aggregation for the observed dependence on concentration is given.

Bacteriorhodopsins↗