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Biomedical subjects

A B Rocha

Publications and source records attributed to A B Rocha.

8 recordsLinked to original sources
PubMed2005

On the conformational memory in the photodissociation of formic acid.

The photodissociation of formic acid at 248 and 193 nm was investigated by classical trajectory and RRKM calculations using an interpolated potential energy surface, iteratively constructed using the B3LYP/aug-cc-pVDZ level of calculation. Several sampling schemes in the ground electronic state were employed to explore the possibility of conformational memory in formic acid. The CO/CO2 branching ratios obtained from trajectories initiated at the cis and at the trans conformers are almost identical to each other and in very good accordance with the RRKM results. In addition, when a specific initial excitation that simulates more rigorously the internal conversion process is used, the calculated branching ratio does not vary with respect to those obtained from cis and trans initializations. This result is at odds with the idea of conformational memory in the ground state proposed recently for the interpretation of the experimental results. It was also found that the calculated CO vibrational distributions after dissociation of the parent molecule at 248 nm are in agreement with the experimental available data.

Journal Article↗
PubMed2000

Retinol-induced changes in the phosphorylation levels of histones and high mobility group proteins from Sertoli cells.

Chromatin proteins play a role in the organization and functions of DNA. Covalent modifications of nuclear proteins modulate their interactions with DNA sequences and are probably one of the multiple factors involved in the process of switch on/off transcriptionally active regions of DNA. Histones and high mobility group proteins (HMG) are subject to many covalent modifications that may modulate their capacity to bind to DNA. We investigated the changes induced in the phosphorylation pattern of cultured Wistar rat Sertoli cell histones and high mobility group protein subfamilies exposed to 7 microM retinol for up to 48 h. In each experiment, 6 h before the end of the retinol treatment each culture flask received 370 KBq/ml [32P]-phosphate. The histone and HMGs were isolated as previously described [Moreira et al. Medical Science Research (1994) 22: 783-784]. The total protein obtained by either method was quantified and electrophoresed as described by Spiker [Analytical Biochemistry (1980) 108: 263-265]. The gels were stained with Coomassie brilliant blue R-250 and the stained bands were cut and dissolved in 0.5 ml 30% H2O2 at 60oC for 12 h. The vials were chilled and 5.0 ml scintillation liquid was added. The radioactivity in each vial was determined with a liquid scintillation counter. Retinol treatment significantly changed the pattern of each subfamily of histone and high mobility group proteins.

Animals↗
PubMed1997

Influence of the biomatrix on the response of Sertoli cells to FSH.

Sertoli cell preparations isolated from 15-day-old Wistar rats were cultured on two different substrates, i.e., plastic and a biomatrix isolated from seminiferous tubules of rat testis. Sertoli cells cultured on a biomatrix acquired a phenotype and morphology more characteristic of in vivo differentiated cells. In order to determine the influence of a biomatrix on the response of Sertoli cells to FSH, on the 7th day of culture, untreated cells, or cells pretreated for 12 h with FSH (1 microgram/ml), were incubated with [U-14C] leucine or [2-3H] mannose. Cells cultured on the biomatrix showed higher [U-14C] leucine and [2-3H] mannose incorporation into proteins and glycoproteins. FSH increased these activities in cells cultured on both substrates, although its stimulating effect was higher on cells cultured on the biomatrix. These results demonstrate that the biomatrix increases protein and glycoprotein synthesis and secretion, and also influences the response of Sertoli cells to FSH.

Animals↗
PubMed1994

Biomatrix effect on Sertoli cells phospholipids.

In order to investigate the influence of biomatrix on Sertoli cell morphology and on the phospholipids content, these cells were isolated from testes of 15-day old Wistar rats and plated onto plastic coated with extracellular matrix extracted from seminiferous tubules, here denoted biomatrix. When the Sertoli cells were cultured on biomatrix they did not form a monolayer until day 7 of culture, while cells plated onto plastic did so 48 h after plating. On day 5 of culture, Sertoli cells were incubated for 48 h with 5 microCi/ml 32P. There was no difference in 32P incorporation into lipids of cells plated onto biomatrix or plastic. However, there was a larger amount of phospholipid phosphate in cells plated onto biomatrix than onto plastic. When the phospholipids were analyzed by bidimensional thin-layer chromatography, no differences were detected in their distribution; however, there was a significant decrease in the percentage of sphingomyelin in cells plated onto biomatrix when compared to plastic. These results showed that the cells cultured on biomatrix change their phospholipids content, but not their distribution. The importance of a small reduction in sphingomyelin content remains to be investigated.

Animals↗