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Biomedical subjects

A A Razak

Publications and source records attributed to A A Razak.

18 recordsLinked to original sources
PubMed1998

Alteration of cell-wall composition of Fusarium oxysporum by copper stress.

A strain of Fusarium oxysporum tolerated copper in the growth medium at concentrations up to 600 mg/L. The optimum growth was obtained at 200 mg Cu/L. The mycelium acquired a blue color in the presence of copper. The copper content of isolated cell walls obtained from mycelium grown in the presence of 600 mg Cu/L was 1.5 times higher than that of cell walls obtained from mycelium grown at 200 mg Cu/L and it contained 2.2 and 3.3% copper at 200 and 600 mg Cu/L, respectively. The amount of protein and total sugars increased in both the mycelium and its isolated cell walls in the presence of copper in the growth medium, chitin was also increased in the cell wall, reaching its maximum amount at 200 mg Cu/L--about 2.4 times higher than without copper. Most of amino acid concentrations in the cell wall were increased in the presence of 200 mg Cu/L and decreased above this concentration. Isoleucine, leucine, tyrosine, phenylalanine, and arginine showed the highest increase at this concentration. The altered cell walls obtained from mycelium grown at 200 and 400 mg Cu/L could rebind individual metals more than the control cell walls could. Rebinding of individual metals was in the order Zn > Fe > Ni > Cu > Co. Rebinding of copper by isolated cell walls depended on pH and temperature.

Amino Acids↗
PubMed1997

The effect of filler content and processing variables on dimensional accuracy of experimental composite inlay material.

STATEMENT OF PROBLEM: Dimensional accuracy of a composite inlay restoration is important to ensure an accurate fit and to minimize cementation stresses. PURPOSE OF STUDY: A method was developed to measure dimensional accuracy and stability of a composite inlay. MATERIAL AND METHODS: A standard Class II (MOD) inlay cavity stainless steel mold was made with six circular indentations placed on the occlusal floor of the cavity and four indentations on each gingival floor to act as datum points in the measurement of linear polymerization shrinkage. The inlay restorations were prepared from an inlay-onlay composite material of different filler contents (50%, 65%, and 79% by weight). For each filler content group, three curing methods were used: light curing only, light curing and heat curing at 100 degrees C for 5 minutes, and light curing and heat curing at 100 degrees C for 5 minutes and then storage in distilled water for 7 days. The accuracy of the MOD inlays was determined by measuring the shrinkage of the restoration on the occlusal floor areas and the gingival seats. RESULTS: The results demonstrated an inverse linear relationship between filler content and polymerization shrinkage. There was a tendency for the light-curing and heat-curing method to show an increase in polymerization shrinkage. An expansion was recorded between the mesial and distal boxes when the specimens were soaked in water for 7 days. CONCLUSIONS: This study suggested that the inlay mold limits the physical shrinkage that can occur between the mesial and distal axial walls of the inlay restoration because the inlay cannot shrink to a smaller dimension than the mold. Water sorption then causes hygroscopic expansion, which enlarges the distance between the mesial and distal walls.

Analysis of Variance↗
PubMed1997

The optimum curing cycle for a light- and heat-cured composite inlay material.

The transverse bend test and surface microhardness test were used to determine the optimum curing cycle for a light- and heat-cured composite inlay material. Specimens were light-cured (control) and light- and heat-cured using the following temperatures: 50 degrees C for 5 min; 50 degrees C for 10 min; 100 degrees C for 1 min; 100 degrees C for 5 min; 100 degrees C for 10 min; and 100 degrees C for 15 min. Heat-curing in boiling water at 100 degrees C for at least 1 min significantly improved the transverse strength, modulus of elasticity and surface microhardness compared to light-curing only or at 50 degrees C. The curing cycle of 100 degrees C for 5 min is considered the most appropriate.

Analysis of Variance↗
PubMed1996

Effect of fungistatic agent 2-deoxy-D-glucose on mycotoxins from Penicillium expansum.

Mycotoxin production from Penicillium expansum was effected by the 'biocontrol enhancer' 2-deoxy-D-glucose (DOG). Citrinin and gentisyl alcohol were produced in higher amounts, whereas patulin was inhibited, which represents a differential effect on the polyketide metabolic pathway. These effects have implications for the use of DOG in biocontrol.

Antimetabolites↗
PubMed1991

Influence of selenium on the efficiency of fungicide action against certain fungi.

Aspergillus funiculosus was isolated from rotted banana fruits, whereas Alternaria tenuis and Fusarium sp. were isolated from rotted tomato fruits. The isolated fungi tolerated relatively high levels of the fungicide, Dithane, up to 2560 ppm on solid medium, but grew well at 40 ppm when supplemented with liquid medium. They are able to tolerate selenite up to 2% (w/v) sodium selenite. A. funiculosus showed no growth in the presence of mixture of 2.5 ppm selenium and 20 ppm Dithane, whereas Fusarium sp. failed to grow at 2.5 ppm selenium and 10 ppm Dithane, or at 10 ppm of each. Nevertheless, Alternaria tenuis is more tolerant; it showed growth in the presence of relatively high levels of selenium and Dithane; up to 10 ppm selenium and 40 ppm Dithane, however, its growth was inhibited by the presence of a mixture of both. The results suggested new form of highly active fungicides. Selenium as an essential nutrient at such very low concentrations, as well as the application of very low concentrations of the fungicide, would certainly reduce the hazardous effect of such pollutant in the environment.

Alternaria↗
PubMed1991

Cadmium, selenium, and tellurium chelators in Aspergillus terreus.

Aspergillus terreus was cultivated on Harrold's medium supplemented with 0.1% (w/v) cadmium chloride as well as on sulfur free medium amended with 0.1% (w/v) sodium selenite and potassium tellurite separately. The cell free extract of the fungus for each treatment was fractionated on a column packed with Sephadex G 75. The results demonstrated the ability of the fungus to synthesize several cadmium, selenium, and tellurium-binding proteins as well as metallothionein. The results suggested the biosynthesis of heavy metals chelators as well. The amino acids composition of a cadmium-binding metallothionein revealed the presence of high levels of both aromatic and sulfur amino acids in the hydrolysate.

Amino Acids↗
PubMed1990

Metabolism of selenium in a selenium-dependent bacterium.

A selenium-dependent Bacillus sp. is able to grow well up to 3% sodium selenite-containing media. The bacterium completely failed to grow on media devoid of selenium. The presence of selenium in the growth media increased the bacterial contents of proteins, carbohydrates, and lipids. The highest quantities of amino acids were detected at 2% sodium selenite-containing media. The bacterium metabolized selenite into several protein selenoamino acids such as selenomethionine and selenocysteine/selenocystine, as well as nonprotein selenoamino acids, such as selenocystathionine. Several phosphoamino acids were detected in the presence of elevated levels of selenium. The synthesized protein seems not to be affected by the presence of selenium.

Amino Acids↗
PubMed1990

Mobilization of selenium by a selenium-dependent bacterium.

A selenium-dependent bacterium, Bacillus sp., failed to grow on selenium-free media. However, it is able to grow at high concentrations of sodium selenite containing media up to 3% (w/v). It accumulated extraordinary high quantities of selenium, 432 ppm/mL. The bacterium generated the transformation of inorganic selenium into volatile selenium form(s) into the atmosphere. The biological release of volatile selenium basically depended on several factors: incubation temperature, pH, incubation periods, and substrate concentration. Maximal quantity of the volatile selenium form was obtained at 30 degrees C, pH 7, and 1% (w/v) sodium selenite.

Bacillus↗
PubMed1989

Incorporation of cadmium into proteins in a cadmium tolerant fungi.

Aspergillus carbonarius and a strain of Penicillium, a cadmium tolerant fungi, are able to metabolize cadmium chloride up to 2% (w/v). Their amino acids analysis on cadmium free and cadmium chloride containing media indicated certain disorders in their metabolic activities. Cystathionine was only detected in both fungi in the presence of cadmium chloride. However, cadmium was incorporated into several types of low and high molecular weight proteins. The amino acids hydrolyzates of a cadmium containing protein are characterized by the presence of high levels of sulfur amino acids; cysteine and methionine. Ethylasparagine was detected in the hydrolyzate of that cadmium containing protein as well.

Amino Acids↗
PubMed1989

Incorporation of tellurium into amino acids and proteins in a tellurium-tolerant fungi.

Aspergillus fumigatus, Aspergillus terreus, and Penicillium chrysogenum, a tellurium tolerant fungi, are able to grow on sulfur free medium amended with 0.2% (w/v) tellurite. Tellurium was incorporated into several types of low and high molecular weight proteins. The newly detected telluro-proteins contained an extraordinary high level of tellurium, as well as telluro-cysteine, telluro-cystine, telluro-methionine, and serine.

Amino Acids↗
PubMed1988

Selenium metabolism in a strain of Fusarium.

Fusarium sp. was isolated from Sinai soil at Egypt. It showed tendency to tolerate high concentrations of selenium in the form of sodium selenite up to 3.5% (w/v). The microscopic examination revealed some morphological distortions. However, the fungus was capable to circumvent the toxic effect of selenium. The fungus possess strong reducing ability as high quantities of elemental selenium were precipitated within the fungal cells as well as on the surface of the fungal hyphae and spores. The presence of selenium increased the cellular contents of carbohydrates, proteins, and lipids. Labeling studies indicate the incorporation of selenite into certain amino acids: selenocysteine and selenocysteic acid. Moreover, the presence of selenium induced the biosynthesis of several types of low molecular weight proteins. The results demonstrated different modes of detoxification of selenium toxicity.

Fusarium↗
PubMed1988

Selenoprotein in Aspergillus terreus.

Aspergillus terreus, a moderately selenium-tolerant fungus, metabolized Se-selenite into several protein seleno-amino acids: selenomethionine and selenocysteine, as well as, nonprotein seleno-amino acids, selenocystathionine, and y-glutamyl selenomethyl selenocysteine. The results indicate the failure of the fungus to discriminate between sulphur and selenium. Selenium was also incorporated into several proteins of different molecular weights, mostly of low molecular weight proteins. Labeled studies showed the presence of high levels of selenomethionine and selenocysteine in the protein hydrolysate. The actual incorporation of protein seleno-amino acids into the fungal protein was proven. The results demonstrated a finding that detracts from previous held views.

Aspergillus↗
PubMed1988

Influence of cadmium on certain biological activities in a cadmium-tolerant fungi.

Aspergillus carbonarius and a strain of Penicillium are able to grow on Harrold's agar media amended with different concentrations of cadmium chloride up to 2.5% (w/v). Considerable quantities of cadmium were absorbed by both fungi. A. carbonarius absorbed more cadmium than the Penicillium sp. did, under the same culturing conditions. In the presence of cadmium, the determined cellular contents of proteins, lipids, and carbohydrates were extraordinary high, whereas the activities of certain enzymes, lipases, amylases, and proteases were inhibited. The fungal rate of growth and sporulations were mostly suppressed. Conidiations were inhibited at lowest concentrations. At 1% Cd Cl2, A. carbonarius produced malformed conidiophores, whereas the Penicillium sp. was less affected. At higher concentrations conidiophores production were entirely suppressed and several hyphal swellings were produced.

Aspergillus↗
PubMedDate not supplied

Some mechanical properties of a highly cross-linked, microwave-polymerized, injection-molded denture base polymer.

PURPOSE: The impact strength and the flexural properties of denture base materials are of importance in predicting their clinical performance upon sudden loading. This study compares the impact and transverse strengths and the flexural modulus of three denture base polymers. MATERIALS AND METHODS: The investigation included a relatively new microwave-polymerized polyurethane-based denture material processed by an injection-molding technique, a conventional microwave-polymerized denture material, and a heat-polymerized compression-molded poly(methyl methacrylate) (PMMA) denture material. Impact strength was determined using a Charpy-type impact tester. The transverse strength and the flexural modulus were assessed with a three-point bending test. The results were subjected to statistical analysis using a one-way analysis of variance and the Scheffé test for comparison. RESULTS: The impact strength of the microwave-polymerized injection-molded polymer was 6.3 kl/m2, while its flexural strength was 66.2 MPa. These values were lower than those shown by the two compression-molded PMMA-based polymers. The differences were statistically significant. The flexural modulus of the new denture material was 2,832 MPa, which was higher than the conventional heat-polymerized polymer but was comparable to the other microwave-polymerized PMMA-based polymer. The difference in the flexural modulus was statistically significant. CONCLUSION: In terms of the impact and flexural strengths, the new microwave-polymerized, injection-molded, polyurethane-based polymer offered no advantage over the existing heat- and microwave-polymerized PMMA-based denture base polymers. However, it has a rigidity comparable to that of the microwave-polymerized PMMA polymer.

Acrylic Resins↗