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Biomedical subjects

R de Souza Pereira

Publications and source records attributed to R de Souza Pereira.

6 recordsLinked to original sources
PubMed2001

The use of calcium blockers to study biochemical behaviour of Saccharomyces cerevisiae cells.

Calcium channel blockers, currently used in clinical medicine, from the dihydropyridine class (nifedipine and nimodipine) were used to study biochemical behaviour of Saccharomyces cerevisiae cells. At a concentration of 200 microM, both drugs partially blocked calcium uptake from an extracellular medium. On the other hand, nifedipine (300 microM) induced a collapse of the membrane potential (delta psi) of these cells, while nimodipine, at the same concentration, produced a similar but less intense effect. Probably, the small difference in the chemical structure between these drugs may explain the same effect with different intensity. With these experiments was possible to observe that these microorganisms have type 'L' calcium channels.

Calcium↗
PubMed2000

Detection of the absorption of glucose molecules by living cells using atomic force microscopy.

A very small electrode (nanobiosensor) was constructed by immobilizing enzyme (glucose oxidase or hexokinase) on the surface of the cantilever of the atomic force microscope in order to detect the absorption of glucose molecules by living cells. If glucose is present, the nanobiosensor deflects, probably due to the reaction heat evolved in the process. Nanobiosensors built with inactivated enzyme or cantilevers without immobilized enzyme were not capable of producing this type of signal (deflection). This technique will be very useful in detecting the passage of specific molecules through a cell wall (or a cell membrane for other types of cells).

Glucose↗
PubMed1999

Direct observation of oxidative stress on the cell wall of Saccharomyces cerevisiae strains with atomic force microscopy.

We imaged pores on the surface of the cell wall of three different industrial strains of Saccharomyces cerevisiae using atomic force microscopy. The pores could be enlarged using 10 mM diamide, an SH residue oxidant that attacks surface proteins. We found that two strains showed signs of oxidative damage via changes in density and diameter of the surface pores. We found that the German strain was resistant to diamide induced oxidative damage, even when the concentration of the oxidant was increased to 50 mM. The normal pore size found on the cell walls of American strains had diameters of about 200 nm. Under conditions of oxidative stress the diameters changed to 400 nm. This method may prove to be a useful rapid screening process (45-60 min) to determine which strains are oxidative resistant, as well as being able to screen for groups of yeast that are sensitive to oxidative stress. This rapid screening tool may have direct applications in molecular biology (transference of the genes to inside of living cells) and biotechnology (biotransformations reactions to produce chiral synthons in organic chemistry.

Antioxidants↗
PubMed1998

The use of molecular modelling in the understanding of configurational specificity (R or S) in asymmetric reactions catalyzed by Saccharomyces cerevisiae or isolated dehydrogenases.

This method gives a general ideal how to use crystallographic information of enzymes to understand reactions catalyzed by these biocatalysts, commonly used by biochemists to produce chiral products. The interactions of three acetoacetic esters with the enzymes L-lactate dehydrogenase and alcohol dehydrogenase were studied through molecular modelling computer program. These artificial substrates have been widely used to produce chiral synthons. Through this methodology it was possible to understand the conformational specificity of these enzymes with respect to the products and how these enzymes can be inhibited by modifying the structures of the artificial substrates. Also, it was possible to predict whether some type of artificial substrate will suffer reduction by cells that contain these dehydrogenases and what kind of configuration (R or S) the final product will have.

Catalysis↗
PubMed1998

Comparison of biochemical effects produced by calcium ions and by monomers of polyacrylamide (acrylamide and bisacrylamide) on strains of Saccharomyces cerevisiae used for production of chiral synthons.

The biochemical behaviour of four commercial strains of Saccharomyces cerevisiae was studied in the presence of calcium ions, acrylamide and bisacrylamide. Calcium ions at a concentration of 300 microM induced an increase of NAD(P)+ reduction in commercial Turkish and American strains, while in Chilean and Brazilian commercial strains, it diminished NAD(P)+ reduction. On the other hand, polyacrylamide monomers (acrylamide and bisacrylamide) induced a decrease of NAD(P)+ reduction in all strains studied in this paper. When membrane potential (delta psi) and oxygen consumption were measured in the presence of polyacrylamide monomers, a decrease of both was observed in all strains studied.

Acrylamides↗