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Biomedical subjects

F Sarhan

Publications and source records attributed to F Sarhan.

32 records · Page 2Linked to original sources
PubMed1992

A molecular marker to select for freezing tolerance in Gramineae.

We isolated, and expressed in Escherichia coli, a gene (Wcs120) that is strongly induced during cold acclimation of wheat. The gene product was purified and used to produce antibodies. Immunoblotting experiments with the anti-WCS120 antibody identified several cold-induced proteins named FTMs for Freezing Tolerance Markers since they are associated with the development of freezing tolerance. This protein family was found to be coordinately regulated specifically by low temperature, highly hydrophilic, stable to boiling, and to have a pI above 6.5. The accumulation kinetics during the acclimation period indicated a positive correlation with the capacity of each genotype to develop freezing tolerance. Accumulation of the proteins was higher in the freezing-tolerant genotype than in the less tolerant one. In addition, their accumulation was more pronounced in the crown and leaf tissues compared with roots, confirming a relationship to the capacity of the different tissues to develop freezing tolerance. Analysis of different species (eight monocots and four dicots) indicated that this protein family is specific for freezing-tolerant cereals. The antibody did not cross-react with any of the non-cereal species examined. The anti-FTMs antibody represents a potential tool for breeders to select for freezing tolerance traits in the Gramineae.

Adaptation, Physiological↗
PubMed1992

Cloning, characterization, and expression of a cDNA encoding a 50-kilodalton protein specifically induced by cold acclimation in wheat.

We have isolated, sequenced, and expressed a cold-specific cDNA clone, Wcs120, that specifically hybridizes to a major mRNA species of approximately 1650 nucleotides from cold-acclimated wheat (Triticum aestivum L.). The accumulation of this mRNA was induced in less than 24 hours of cold treatment, and remained at a high steady-state level during the entire period of cold acclimation in the two freezing-tolerant genotypes of wheat tested. The expression of Wcs120 was transient in a less-tolerant genotype even though the genomic organization of the Wcs120 and the relative copy number were the same in the three genotypes. The mRNA level decreased rapidly during deacclimation and was not induced by heat shock, drought, or abscisic acid. The Wcs120 cDNA contains a long open reading frame encoding a protein of 390 amino acids. The encoded protein is boiling stable, highly hydrophilic, and has a compositional bias for glycine (26.7%), threonine (16.7%), and histidine (10.8%), although cysteine, phenylalanine, and tryptophan were absent. The WCS120 protein contains two repeated domains. Domain A has the consensus amino acid sequence GEKKGVMENIKEKLPGGHGDHQQ, which is repeated 6 times, whereas domain B has the sequence TGGTYGQQGHTGTT, which is repeated 11 times. The two domains were also found in barley dehydrins and rice abscisic acid-induced protein families. The expression of this cDNA in Escherichia coli, using the T(7) RNA polymerase promoter, produced a protein of 50 kilodaltons with an isoelectric point of 7.3, and this product comigrated with a major protein synthesized in vivo and in vitro during cold acclimation.

Journal Article↗
PubMed1990

Localization of vitamin B12 binding in Euglena gracilis.

Different fractionation procedures were used to determine the location of vitamin B12 binding sites in Euglena gracilis. Using uptake measurements, cell fractionation, and light and electron microscopy, the cuticle of the cell was found to be the fraction containing the majority of B12 binding sites. The apparent distribution of vitamin binding sites differed according to the cell lysis method used. The cuticle fraction was responsible for the binding of 80% of the vitamin taken up by the cell during both the rapid and the slow phase of uptake. These results suggest that vitamin B12 binding is regulated, in part, at the cuticle level, and support our previous conclusion that the secondary phase of uptake represents the synthesis of new receptor sites and not the unloading of vitamin inside the cell.

Animals↗
PubMed1989

Synthesis of Freezing Tolerance Proteins in Leaves, Crown, and Roots during Cold Acclimation of Wheat.

Protein synthesis was studied in leaves, crown, and roots during cold hardening of freezing tolerant winter wheat (Triticum aestivum L. cv Fredrick and cv Norstar) and freezing sensitive spring wheat (T. aestivum L. cv Glenlea). The steady state and newly synthesized proteins, labeled with [(35)S]methionine, were resolved by one- and two-dimensional polyacrylamide gels. The results showed that cold hardening induced important changes in the soluble protein patterns depending upon the tissue and cultivar freezing tolerance. At least eight new proteins were induced in hardened tissues. A 200 kilodalton (kD) (isoelectric point [pl] 6.85) protein was induced concomitantly in the leaves, crown, and roots. Two proteins were specifically induced in the leaves (both 36 kD, pl 5.55 and 5.70); three in the crown with M(r) 150 (pl 5.30), 45 (pl 5.75), and 44 kD (pl > 6.80); and two others in the roots with M(r) 64 (pl 6.20) and 52 kD (pl 5.55). In addition, 19 other proteins were synthesized at a modified rate (increased or decreased) in the leaves, 18 in the crown and 23 in the roots. Among the proteins induced or increased in hardened tissues, some were expressed at a higher level in the freezing tolerant cultivars than in the sensitive one, indicating a correlation between the synthesis and accumulation of these proteins and the degree of freezing tolerance. These proteins, suggested to be freezing tolerance proteins, may have an important role in the cellular adaptation to freezing.

Journal Article↗
PubMed1988

In vitro effect of aflatoxin B1 on the transcriptional activity of DNA template, chromatin and soluble DNA-dependent RNA polymerases in buffalo liver.

The effect of aflatoxin B1 on the DNA template and DNA-dependent RNA polymerases in buffalo liver was studied. Aflatoxin B1 inhibited both Mg2+- and Mn2+-activated RNA polymerases in a dose-dependent manner. At 10 micrograms the inhibition of both enzymes was almost complete. The inhibitory effect on the solubilized enzymes was higher than the chromatin-bound, suggesting a direct effect at the enzyme level. On the other hand, incubating DNA or deoxyribonucleoprotein (DNP) with 2 micrograms aflatoxin reduces its transcriptional capacity with a greater effect on the Mg2+-activated RNA polymerase than the Mn2+-activated enzyme. These results suggest that aflatoxin B1 inhibits in vitro transcription in buffalo liver at both enzyme and template levels.

Aflatoxin B1↗
PubMed1985

Regulation of RNA Synthesis by DNA-Dependent RNA Polymerases and RNases during Cold Acclimation in Winter and Spring Wheat.

Chromatin DNA-dependent RNA polymerases and RNases activities were measured in winter and spring varieties to understand the overall regulation of RNA synthesis during cold acclimation. We found that total RNA polymerase activities were significantly higher in chromatin isolated from winter wheat compared to the spring wheat during the acclimation period. This increase was parallel to the increase in protein and RNA contents during hardening. The ratio of RNA polymerase I to RNA polymerase II activity was higher than 2 in winter wheat after 30 days of hardening compared, to a ratio of 0.90 under the nonhardening conditions. The increase in activity and the ratio of polymerase I to polymerase II was maintained after the separation of the enzymes from the template, suggesting that RNA synthesis is regulated in part at the enzyme level. On the other hand, the chromatin associated RNase activity decreased in both varieties during acclimation, indicating a nonspecific inhibition caused by low temperature rather than a selective genetic response associated with cold acclimation.

Journal Article↗
PubMed1981

Distribution, metabolism, and elimination of phenobarbital in rats: physiologically based pharmacokinetic model.

The distribution, metabolism, and elimination kinetics at two different doses of phenobarbital were examined in rats. After intravenous injection, phenobarbital distributed very rapidly to the liver and kidneys, less rapidly to the muscle and gut, and much more slowly to the brain. At the higher dose, a concentration rebound was observed 1 hr after injection. In addition, phenobarbital distributed unevenly in various organs as a result of a different extent of drug binding. A physiologically based model, including enterohepatic cycling and diffusion resistances between blood and tissue, is proposed for phenobarbital pharmacokinetics. It satisfactorily describes phenobarbital distribution in rats at the two doses and allows an evaluation of fundamental physicobiochemical parameters such as drug-tissue binding constants, blood-tissue transport coefficients, metabolism, and elimination rate constants.

Animals↗
PubMed1981

Effect of diphenylhydantoin and its main hydroxylated metabolite on the pharmacokinetics and the urinary and biliary excretion of phenobarbital and its p-hydroxy metabolite.

When rats which had been pretreated with a high dose of diphenylhydantoin (80 mg/kg) for 5 days were given a single intravenous dose of phenobarbital (30 mg/kg): (a) There was no increase in the rate at which phenobarbital (PB) disappeared from the plasma or the tissues of pretreated rats. (b) The percentages of phenobarbital and p-hydroxyphenobarbital (free and conjugated) excreted in the urine were similar in both treated and control animals. However, the percentage of conjugated p-hydroxyphenobarbital excreted, was almost twice that of the control group. (c) Pretreatment with diphenylhydantoin (DPH) markedly increased bile flow rates. Therefore these rats excreted more PB than their controls. The biliary excretion of hydroxylated metabolites of PB (free and conjugated), was similar to that found in urine. Hydroxylation was not increased although, there was a significant elevation in the percentage of conjugated metabolite excreted. In a study to establish whether the main metabolites of diphenylhydantoin interfered with the metabolism of phenobarbital the following results were obtained: (a) Intravenous administration of DPH together with PB caused a two-fold increase in the half-life of phenobarbital elimination. (b) Intravenous administration of PB, to bile duct cannulated rats which had been pretreated for 5 days with DPH, caused a significant reduction in the excretion of hydroxylated phenobarbital in comparison with their control group. However, all the excreted DPH was present in the conjugated form. (c) The DPH pretreated rats had significantly lower cytochrome P-450 and mono-oxygenase activities in their hepatic microsomes than the pretreated controls, and higher UDP-glucuronyltransferase activity with DPH itself as the substrate.

Animals↗
PubMed1978

Induction of deoxyribonucleic acid degradation in Escherichia coli by ozone.

Cell survival and deoxyribonucleic acid (DNA) degradation wave measured for wild-type Escherichia coli B251 cells after exposure to different concentrations of ozone. The results show that extensive breakdown of DNA occurs after ozonation and that the extent of ozone-induced DNA degradation generally correlates with the colony-forming ability of the cells.

DNA, Bacterial↗
PubMed1978

[Comparative effects of antiepileptics on the alkaline phosphatase and gamma glutamyltransferase activities in plasma and leukocytes].

Alkaline phosphatase and gamma glutamyltransferase activities have been compared in plasma and leukocytes from presumably healthy subjects and from epileptic patients under treatment with different antiepileptic drugs. Plasma enzyme activities are always increased by antiepileptic treatment, leukocytic enzyme activities are increased only for some patients. No relation has been observed between the variations in any of the two enzyme activities and plasma level of anticonvulsant drugs.

Alkaline Phosphatase↗
PubMedDate not supplied

Gene expression during cold and heat shock in wheat.

Translatable messenger RNAs expression was compared in cold- and heat-stressed winter wheat (Triticum aestivum L. 'Fredrick' and 'Norstar') and spring wheat (T. aestivum L. 'Glenlea'). Polyadenylated RNA isolated from the crown and leaf tissues was translated in a wheat germ cell free system and the acidic and basic in vitro products were resolved by two-dimensional SDS-PAGE and autoradiography. The results showed that low temperature stress rapidly induced two groups of mRNAs. The first group was transient in nature and consists of 18 mRNAs that reached their highest levels of induction after 24 h of low temperature exposure and then decreased to undetectable levels. The second group consists of 53 mRNAs that were also induced or increased rapidly, but maintained their levels of expression during the 4 weeks required to induce freezing tolerance. Among those, at least 34 were expressed at higher levels in the freezing tolerant winter wheat compared with the less tolerant spring wheat. This suggests a possible relation between the expression of these mRNAs and the capacity of each genotype to develop freezing tolerance. In the case of heat shock, 50 mRNAs were induced or increased after 3 h at 40 degrees C. Among these, the expression of only six mRNAs was altered in a similar manner in the three genotypes by both treatments. The remaining mRNAs code for typical heat shock proteins which are different from those induced by low temperature. None of these mRNAs has been associated with the development of freezing tolerance. These results suggest that heat and cold stress are controlled by different genetic systems.

Autoradiography↗