PubMed Health⌕ Search

Biomedical subjects

M Belli

Publications and source records attributed to M Belli.

At least 73 records · Page 4Linked to original sources
PubMed1989

RBE-LET relationship for the survival of V79 cells irradiated with low energy protons.

The survival of V79 Chinese hamster cells irradiated with proton beams with energies of 0.73, 0.84, 1.16, 1.70 and 3.36 MeV, corresponding to LET values, evaluated at the cell midplane, of 34.5, 30.4, 23.9, 17.8 and 10.6 keV/micron respectively, have been studied in the dose range 0.5-6.0 Gy. As a reference, the survival curve obtained with 200 kV X-rays was used. The initial shoulder, typical of survival curves obtained with sparsely ionizing radiation, decreases as the LET increases and completely disappears at 23.9 keV/micron. This value corresponds to the maximum of the RBE, expressed as the initial slope ratio. In the energy range we have considered, the RBEs for protons are higher than those reported for other ions of comparable LET and the RBE-LET relationship results shifted to lower LET values. Our data seem to indicate that the RBE-LET curve depends on the type of radiation and this could imply that LET is not a good reference for the dose-effectiveness relationship.

Animals↗
PubMed1989

Behaviour of adenylic and pyridinic compounds in gingival tissue after a short-term exposure to air.

Biochemical variations of adenine and pyridine compounds in human gingival grafts during the period between excision and implantation have been studied. These groups of compounds are considered as "indicators" of the metabolic and energetic status of the living cells. Adenylic compounds such as ATP, ADP and AMP are involved in numerous metabolic processes as "modulators" of allosteric enzymes. NAD+ and NADP+ are involved in the carbohydrate metabolism as co-factors of many reactions of oxydoreduction. The exposure to air of the gingival tissue induces modifications in the energy state of the cells as well as in the ox-reox system. No variation is detectable in the intermediates of the pyridine compounds cycle.

Adenine Nucleotides↗
PubMed1989

Radiation damage and chromatin structure.

The recent advances made in the knowledge of chromatin structure have important implications in molecular and cellular radiobiology. There are now many lines of evidence that the chromatin organization can affect the production, the distribution and the repair of radiation-induced damage in DNA. Experiments with polynucleosomes show that DNA double strand breaks (dsb) are not randomly distributed along the DNA molecule. Rather, they are preferentially localized in linker regions, while core regions are more resistant. Isolated DNA is about 4-fold more susceptible to dsb than DNA irradiated as a part of polynucleosomes. This differential radiosensitivity is apparently due to the close association of DNA with proteins. The analysis of DNA single strand breaks production and repair in a human erythroleukemic cell line that can be induced to differentiate in vitro, showed that the repair kinetics in differentiated cells appears significantly slower than in undifferentiated ones. This can be interpreted as a decrease in the genome accessibility to repair enzymes due to the presence of more structured regions in chromatin after differentiation. It appears that a high degree of genome compactness could imply, on one hand, a high DNA radioresistance and, on the other hand, a slow DNA repair so that the identification of chromatin domains which are critical, from the structural point of view, in determining cellular effects such as cell killing and mutation, should take into account a sort of balance between the amount of damage and the extent of repair.

Animals↗
PubMed1986

Hepatitis B virus infection in multitransfused haemophiliacs.

A longitudinal study of 44 haemophilic children, all in a treatment programme with factor concentrates, was undertaken to evaluate the occurrence, characteristics, and evolution of hepatitis B virus (HBV) infection. Twenty four children (55%) (group I) showed signs of HBV infection, while 20 (45%) (group II) did not. Age at onset of treatment, number of infusions, and total amount of concentrate received did not show significant differences between the two groups. In group I only four children (16%) had symptomatic acute hepatitis. Chronic liver disease was present in nine patients (38% of infected children). The early age of infection would seem to be an important factor for predicting chronic evolution. Evidence of delta infection in three children with severe liver disease seemed to confirm the high pathogenicity of this agent. Because of the risks associated with chronic HBV infection a careful follow up of patients positive for hepatitis B surface antigen is mandatory.

Age Factors↗
PubMed1976

Unfolding of E. coli ribosomes: evidence for pre-existing breaks in the large subunit.

An investigation has been made on structure modifications of E. coli ribosomes following EDTA treatment. When completely deprived of magnesium, the small subunit sediments at 16S while the large one, in the same conditions, shows two components at 17S and 21S. Unfolding causes in both subunits an increase in radius of gyration without substantial change in molecular weight, as shown by light scattering measurements. The occurence of the slower 17S component besides the 21S one has to be connected with a fraction of the large subunit population which presents nucleolytic breaks in its RNA chain. These breaks do not cause fragmentation of the unfolded subunit but lead to a more open configuration sedimenting at lower velocity.

Edetic Acid↗
PubMed1975

The secondary structure of E. coli ribosomes and ribosomal RNA's: a spectrophotometric approach.

The thermal denaturation spectra of E. coli 50s and 30s ribosomal sub units and of their isolated RNA's were studied over the wavelength range of 2300-3000 Angstrom. It was possible to fit the experimental denaturation spectra with super positions of the reference spectra for denaturation of A - U and G - C base pairs derived from model polyribonucleotides. The coefficients of these linear combinations were used to calculate the fractions of A - U and G - C base pairs in the samples. It was found that the helical content of the RNA's inside the subunits is smaller than that of the isolated RNA's, thus suggesting that proteins may affect the secondary structure of RNA in the ribosome.

Escherichia↗