Search PubMed⌕ Search

Biomedical subjects

S Stefanini

Publications and source records attributed to S Stefanini.

At least 55 records · Page 3Linked to original sources
PubMed1985

Differentiation of liver peroxisomes in the foetal and newborn rat. Cytochemistry of catalase and D-aminoacid oxidase.

Organules containing cytochemically detectable amounts of catalase and D-aminoacid oxidase activities are observed between the 14th and 21st day of development in the parenchymal cells of the foetal rat liver and in the liver of newborn rats. As early as 14 to 15 days, a limited number of small microperoxisomes, scattered in the cytoplasm of very few hepatocytes, can be found. These are roundish shaped, have a granulous matrix and contain very low, hardly detectable levels of the above mentioned enzymes. In later development both the size and the enzymatic content of the organules gradually increase, approaching adult levels at the end of foetal development. Starting from the 18th to 19th day of intrauterine life nucleoids can be seen in many peroxisomes. The morphological and biochemical maturation from microperoxisomes to peroxisomes is accompanied by a gradual increase in the number of stainable organules, both per individual cell and per tissue area.

Animals↗
PubMed1983

Binding of terbium to apoferritin: a fluorescence study.

Luminescence measurements show that apoferritin binds three Tb(III) atoms per subunit in accordance with crystallographic evidence. Fe(II) competes with Tb(III) for at least some of the binding sites. This competition may be the molecular basis for the inhibition of iron incorporation into apoferritin brought about by Tb(III). Ca(II), which is generally replaced by Tb(III) in Ca(II) binding proteins, does not compete with the lanthanide for binding to apoferritin.

Animals↗
PubMed1982

Structural heterogeneity and subunit composition of horse ferritins.

Structural, spectroscopic, and immunological properties of horse ferritins extracted from spleen, liver, and heart were studied to test the hypothesis that the different tissue ferritins are hybrids composed of variable proportions of two subunit types. The weight-average molecular weights determined by sedimentation velocity and gel filtration increase from 460 000 for spleen to 480 000 for liver and to 515 000 for heart apoferritin; moreover, the diffusion coefficients prove that each tissue-specific ferritin consists of a population of hybrid molecules. The intrinsic fluorescence and the near-UV circular dichroism (CD) spectra change as a function of the subunit composition of the three ferritins. The fluorescence emission maximum, which occurs at a very low wavelength (315 nm) in horse spleen apoferritin, is shifted to increasingly higher wavelengths in the liver and heart proteins (320 and 325 nm, respectively), indicating that the tryptophan and tyrosine residues become less rigidly immobilized with an increase in the H-subunit content. The tryptophan residues behave as fully solvated in the monomeric subunits at acidic pH values. In accordance with the fluorescence data, the near-UV CD spectra show that the tryptophan environment is highly asymmetric in spleen apoferritin, progressively less so in liver and heart apoferritins, and completely relaxed in the dissociated subunits. Moreover, they show that the environment of tyrosines and phenylalanines differs markedly in the spleen and heart apoproteins. The ferritins studied appear to have immunogenic sites which are specific for the H and L subunits on the basis of enzyme-linked immunoassay and double-diffusion experiments.

Animals↗
PubMed1978

Kinetics of iron reduction of ferritin cores and of a low molecular weight hydroxy-iron polymer.

The kinetics of reduction by dithionite of iron cores in ferritin and of iron cores after removal of the protein shell (isolated cores) has been analysed along with that of a low molecular weight hydroxy-iron polymer. Spectrophotometric measurements have shown that the time course of the reaction approximates a pseudo first-order behaviour. In the case of ferritin cores the pseudo first-order rate constant reaches an asymptotic value which markedly increases when the cores are isolated. In contrast, in the low molecular weight hydroxy-iron polymer, no clear asymptotic value is reached. Thus, the rate of reduction appears to be determined both by the presence of the protein shell and by the crystallite surface area. Kinetic light scattering experiments show that in ferritin and in the isolated cores a rapid drop in molecular weight occurs during the first stages of reduction, suggesting a fragmentation of the iron crystallite.

Ferritins↗
PubMed1976

Studies on iron uptake and micelle formation in ferritin and apoferritin.

Iron uptake and micelle formation in ferritin and apoferritin have been followed both spectrophotometrically and by means of sedimentation velocity experiments. Information was thus obtained on the molecular weight distribution of the reconstitution product. To achieve incorporation 'native' ferritin (whole ferritin as purified from horse spleen), 'native' apoferritin (apoferritin prepared by fractionation of ferritin preparations) and 'reduced' apoferritin (apoferritin prepared by reduction of ferritin by dithionite or ascorbic acid) have been incubated with ferrous salts in the presence of oxidizing agents under different experimental conditions. Although some iron is incorporated in 'native' ferritin, full saturation is not achieved and the molecular weight distribution of the incubated products remains heterogeneous. 'Native' and 'reduced' apoferritin show a similar iron incorporation, but the reconstitution products markedly differ in terms of their iron distribution. Ferritin reconstituted from 'native' apoferritin has a broad molecular weight distribution, while that reconstituted from 'reduced' apoferritin is characterized by a narrow, homogeneous molecular weight distribution. However treatment of apoferrition with reducing or oxidizing agents prior to the incubation alters the characteristics of the iron distribution without changing the iron incorporation properties. These results point to a role of the protein moiety not only in iron oxidation, but also in micelle formation.

Animals↗