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Biomedical subjects

G Geraci

Publications and source records attributed to G Geraci.

At least 55 records · Page 3Linked to original sources
PubMed1984

Studies on the metabolic effects of methylthioformycin.

5'-Methylthioformycin, a structural analog of 5'-methylthioadenosine in which the N-C glycosidic bond is substituted by a C-C bond, has been synthesized by a newly developed procedure. Membrane permeability of the molecule has been compared to that of methylthioadenosine in intact human erythrocytes and Friend erythroleukemia cells. The formycinyl compound is taken up with a rate significantly lower than that of 5'-methylthioadenosine and is not metabolized by the cells. 5'-Methylthioformycin inhibits Friend erythroleukemia cells' growth: the effect is dose-dependent, fully reversible and not caused by cytotoxicity. Several enzymes related to methylthioadenosine metabolism are inhibited by methylthioformycin. Rat liver methylthioadenosine phosphorylase is competitively inhibited with a Ki value of 2 microM. Among the propylamine transferases tested only rat brain spermine synthase is significantly inhibited, while rat brain spermidine synthase is less sensitive. Rat liver S-adenosylhomocysteine hydrolase is irreversibly inactivated with 50% inhibition at 400 microM methylthioformycin. 5'-Methylthioformycin does not exert any significant effect on protein carboxyl-O-methyltransferase. Inferences about the mechanism of the antiproliferative effect of the drug have been drawn from the above results.

Adenosine↗
PubMed1983

High sensitivity method for fluorofore detection in gradient polyacrylamide slab gels through excitation by laser light: application to glycoproteins stained with concanavalin A-fluorescein isothiocyanate.

An easy-to-assemble apparatus for the laser-light excitation of fluorofores in polyacrylamide gels is described. The assemblage is made up of a continuous-wave ion-argon laser with adjustable power output, a beam diffuser, appropriate filters to block excitation light, and a photographic camera. With this setup a minimum 20-fold increase of sensitivity was obtained for fluorofore detection in polyacrylamide gels as compared to the more conventional uv-light excitation using a commercial preparation of Con A-FITC (concanavalin A-fluorescein isothiocyanate) as reference molecule in the gel. The same apparatus, used to analyze the Con A-positive glycoproteins contained in serum Cohn fraction IV separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, showed a number of fluorescent components in a wide range of relative intensities while uv-light excitation showed none. Acrylamide concentration in the gel is critical, since a working limit of between 10 and 12% has been found, above which the diffusion of Con A-FITC in the gel, necessary to label glycoprotein bands, is hampered. The system described here also permits the optimization of detection of minor components not otherwise observable by conventional light excitation, because light power, angle of incidence, and beam divergence can be adapted to analyze specific areas of the sample gel.

Concanavalin A↗
PubMed1983

Histone H1 and chromatin higher order structure. Does histone H1 exhibit specific self-association?

1. Histones H1 and H5 in chromatin and in free solution can be cross-linked to higher multimers. Is this due to a specific protein/protein interaction? If so, this interaction might be the structural basis of the condensation of the chromosomal nucleofilament, known to be mediated by histones H1 and H5. 2. Since only the central domain of H1 and H5 exhibits tertiary folding and globular structure, this is the most likely site of specific interaction. 3. Formaldehyde has been used to test whether the central domains of histone H1 from calf thymus or from sea urchin sperm or histone H5 from chicken erythrocytes self-interact. 4. The cross-linking shown by each globular peptide was compared with that of its parent histone. 5. In all three cases the peptide cross-linked to a much lower extent than its intact parent histone and the observed cross-linked rates were roughly in proportion to the relative number of lysine residues parent histone and peptide. 6. It is concluded that there is no specific self-interaction between the globular domains of either H1 or H5 molecules in free solution. 7. This result suggests that specific H1/H1 protein/protein interactions are not the basic cause of chromatin condensation.

Animals↗
PubMed1983

Synthesis of globin chains in the erythropoietic sites of the early chick embryo.

The synthesis of globins in the chick embryo before the onset of circulation has been studied in situ by specific immunofluorescence labelling of embryonic sections and by labelling newly synthesized proteins in ovo and in vitro in embryonic explants with [3H]leucine. The presence of major primitive haemoglobins is observed by 28 h of incubation. The minor primitive haemoglobins become detectable by immunofluorescence after 40 h of development, shortly before the onset of circulation. 3H-labelling shows that one definitive alpha chain is synthesized, though in low concentration, from the initial globin detection. The other definitive alpha chain is observed in embryos of at least 40 h of development. The relative concentration of the two definitive alpha chains changes rapidly with development indicating a specific mechanism of regulation. An erythropoietic site is observed in the wall of the dorsal aorta in embryos of about 45-50 h of development. From the initial detection, those cells contain all four primitive embryonic haemoglobins, in contrast to what is observed for the cells of the blood islands.

Animals↗
PubMed1981

Preparation and characterization of histone H1 from the sperm of the sea-urchin Sphaerechinus granularis.

The separation and purification of histone H1 from the sperm of the sea-urchin Sphaerechinus granularis is described. Physical studies were used to compare this histone H1 molecule with H1 histones from other species. C.d. and 270 MHz n.m.r. spectroscopy indicate that, despite significant compositional differences from other sea-urchin sperm H1 histones, their secondary and tertiary structures are very similar. A large difference in helicity was, however, found between S. granularis histone H1 and calf thymus histone H1, and their n.m.r. and fluorescence spectra also differ considerably. It is concluded that secondary structure and tertiary structure have not been conserved in the evolution of the H1 histone family.

Amino Acids↗
PubMed1980

Species specificity and individual variability of sea urchin sperm H2B histones.

Total histones from the sperms and embryos of the sea urchins Paracentrotus lividus, Arbacia lixula, Psammechinus microtuberculatus and Sphaerechinus granularis hae been fractionated into the component molecules by electrophoretic analyses in SDS, in urea-acetic acid and in Triton-urea-acetic acid. Sperm H2B histones are in all cases different from those of the corresponding embryonic chromatins. Each sea urchin species has distinctive variants of the sperm H2B histones that are fractionated by electrophoresis in SDS acrylamide gel into two to four components forming a new class of lower mobility. This analytical method shows that individuals of the same species have different assortments of the H2B components. Electrophoretic analyses in Triton-urea also show multiple components for H2B but the patterns are similar in the different individuals.

Animals↗
PubMed1979

The sea urchin (Sphaerechinus granularis) codes different H2B histones to assemble sperm and embryo chromatin.

Histones from sperm and gastrula nuclei of the sea urchin Sphaerechinus granularis were analyzed by three different electrophoretic methods, stained with specific color reactions and compared with one another. The histones of the two cell types showed identical properties in none of the three analytical methods employed but the greatest differences involved the H2B type of histones. H2B from embryo chromatin had properties similar to those of the corresponding molecule from calf thymus. In the sperm chromatin no such molecule was observed but two additional ones were found that differed from embryo H2B in size, charge and specific colour reactions. The differences were such that different genes may be postulated for the synthesis of the H2B histones found in sperm and in embryo.

Animals↗
PubMed1979

DNAase hydrolysis of chromatin DNA in intact sea urchin sperm cells. Effect of the ionic strength on the digestion parameters.

Chromatin DNA in intact functional Sphaerechinus granularis sperm cells has been digested with micrococcal nuclease at three different ionic strength conditions. The results show a highly-flexible chromatin organization similar to that found in sperm heads. The rate of digestion, the limit value of acid-soluble material and the fragmentation pattern show that the sensitivity of nucleosome and internucleosome DNA regions to nuclease hydrolysis depends on a delicate balance of polar and non polar interactions. At low ionic strength, both nucleosome and internucleosome regions are rapidly and completely hydrolysed at the same time and a transient subunit fragment of 120 b.p. average length is formed. At high ionic strength, internucleosome regions are preferentially hydrolysed; there is a limit digest value and a stable subunit fragment of 140 b.p. average length is formed. A supernucleosome organization in the high ionic strength environment of the sperm cells is suggested by the transient preferential formation of heptamers of nucleosome DNA fragments.

Animals↗
PubMed1976

Histidyl-transfer-ribonucleic-acid synthetase from Salmonella typhimurium. Studies of the sulfhydryl groups.

The reactivity of the sulfhydryl groups of histidyl-t RNA synthetase from Salmonella typhimurium and the effect of substrates on the reactivity has been studied using p-hydroxymercuribenzoate and 5, 5'-dithiobis (2-nitrobenzoic acid) as reagents. It has been found that 5, 5'-dithiobis (2-nitrobenzoic acid) titrates only two sulfhydryl groups per molcule of enzyme and the reaction is essenaitlly monophasic, while p-hydroxymercuribenzoate titrates four sulhydryl groups. As observed kinetically the reaction with p-hydroxymercuribenzoate is strongly biphasic, each phase corresponding to about two sulfhydryl groups per enzyme molecule. With both reagents no detectable difference in sulfhydryl group reactivity was observed when ATP, histidine and tRNA specific for histidine were added individually or in combination to the enzyme. The enzyme activity slowly changes after two or four sulhydryl groups are blocked by 5, 5'-dithiobis (2-nitrobenzoic acid) or p-hydroxymercuribenzoate respectively. A new, stable level of activity is reached that is characterized by a different Km value for the aminoacylation reaction. The results indicate that the sulfhydryl groups reacting with the two reagents used here are neither directly involved in the binding of the substrates nor in the catalytic process. The ultimate change in enzyme activity after reaction of the sulfhydryl groups suggests a transition to an alternative enzyme structure.

Amino Acyl-tRNA Synthetases↗
PubMed1976

Chromatin organization in nuclei of sea urchin embryos. Comparison with the chromatin organization of the sperm.

The chromatin in sea urchin embryo nuclei and that in sperm heads are both organized in nucleosomes but show marked differences when analyzed by endonuclease digestion. Sperm chromatin DNA appears to be totally organized in nucleosomes that are highly resistant to nuclease hydrolysis. The kinetics of formation of acid-soluble oligonucleotides is slow and concerns only about 50% of the total DNA. In contrast, the DNA of embryo chromatin does not appear to be totally organized in nucleosomes since 5 to 10% is rapidly and preferentially hydrolysed into acid-soluble oligonucleotides without any appreciable fragmentation of the remaining parts. Futher digestion causes the formation of the usual pattern of DNA bands, as detected by gel electrophoresis. The length of the DNA segment associated with the embryo nucleosomes appears to be shorter than that of the DNA segment associated with the sperm nucleosomes. The kinetics of formation of acid-soluble oligonucleotides upon digestion of embryo chromatin is much faster than that of sperm chromatin and concerns almost all the chromatin DNA.

Animals↗
PubMed1975

The hemoglobins of the developing chicken embryos. Fractionation and globin composition of the individual component of total erythrocytes and of a single erythrocyte type.

The hemoglobins of the chicken embryo at several stages of development have been isolated in pure form by column chromatography and their relative amounts and globin compositions determined. The analyses on separated primitive and definitive erythrocytes show that the first contain four hemoglobins different from the adult ones. The two major ones at four days, decrease gradually and are no longer detectable from 15 days on. The two minor ones increase up to 6-7 days, then decrease but are still present at hatching. The definitive embryonic erythrocytes contain two hemoglobins identical to the adult ones but their ratios change gradually during development and approach that of the adult hemoglobins at hatching.

Animals↗