Biomedical subjects

M A el-Sayed

Publications and source records attributed to M A el-Sayed.

At least 37 records · Page 2Linked to original sources

PubMed1990

Sensitivity of the retinal circular dichroism of bacteriorhodopsin to the mutagenetic single substitution of amino acids: tyrosine.

Bacteriorhodopsin (bR) in the native purple membrane, in wild type expressed in E. coli and reconstituted in lipid vesicles, and its constituted mutants with substitutions of Tyr-185 by Phe all are found to have different visible retinal CD spectra. The results strongly suggest that the environment of the retinal in bR determines the sign and heterogeneity of its visible retinal CD spectrum. This supports the recent proposal that the observed biphasic CD spectrum of bR is due to the superposition of the CD spectra having opposite signs of more than one type of bR rather than due to exciton coupling.

Bacteriorhodopsins↗

PubMed1990

Subpicosecond resonance Raman spectroscopy of carbonmonoxy- and oxyhemoglobin.

In this paper we present the resonance Raman spectrum of the carbonmonoxy- (HbCO) and oxyhemoglobin (HbO2) photointermediates on a 800-900 fs timescale. In the case of HbCO, the frequencies of the so-called core-size markers (1500-1650 cm-1) are characteristic of a deoxylike photoproduct in a high spin state (S = 2) with a partially domed heme. The spectrum of the HbO2 photointermediate, on the other hand, is different, and may be characteristic of an excited-state species. These results are discussed in terms of a reaction scheme previously presented by Petrich, J. W., C. Poyart, and J. L. Martin (1988. Biochemistry. 27:4049-4060) and compared with those obtained in the literature on a 30-40 ps timescale. In both molecules a distinct downshift of the v4 mode was observed with respect to the equilibrium value, which is indicative of an elevated temperature of the heme after photodissociation.

Biophysical Phenomena↗

PubMed1990

Decay of the tryptophan fluorescence anisotropy in bacteriorhodopsin and its modified forms.

In this work we study the decay of the polarization of the Trp fluorescence in native bacteriorhodopsin (bR), deionized bR (dlbR), and the retinal-free form of bR, bacterioopsin (bO), using picosecond laser/streak camera system. Two types of depolarization processes are observed, one around 250 ps, which is temperature independent around room temperature, and the other in the 1-3-ns range, which is sensitive to temperature and certain bR modifications. This suggests the presence of at least two different environments for the eight Trp molecules in bR. Native bR and deionized bR gave the same depolarization decay times, suggesting that the removal of metal cations does not change the microenvironment of the emitting Trp molecules. The slow component is faster in bO than in bR, suggesting a change in the environment of the Trp molecules upon the removal of the retinal chromophore. All these results are discussed in terms of the different mechanisms of Trp fluorescence depolarization. A comparison between the depolarization decay in rhodopsin and bR is made.

Bacteriorhodopsins↗

PubMed1990

Effect of genetic modification of tyrosine-185 on the proton pump and the blue-to-purple transition in bacteriorhodopsin.

The retinylidene chromophore mutant (Y185F) of bacteriorhodopsin, in which Tyr-185 is substituted by phenylalanine, is examined and compared with wild-type bacteriorhodopsin expressed in Escherichia coli; both were reinstituted similarly in vesicles. The Y185F mutant shows (at least) two distinct spectra at neutral pH. Upon light absorption, the blue species (which absorbs in the red) behaves as if "dead"--i.e., neither its tyrosine nor its protonated Schiff base undergoes deprotonation nor does its tryptophan fluorescence undergo quenching. This result is unlike either the purple species (which absorbs in the blue) or wild-type bacteriorhodopsin expressed in E. coli. As the pH increases, both the color changes and the protonated Schiff base deprotonation efficiency suggest a blue-to-purple transition of the Y185F mutant near pH 9. If this blue-to-purple transition of Y185F corresponds to the blue-to-purple transition of purple-membrane (native) bacteriorhodopsin (occurring at pH 2.6) and of wild-type bacteriorhodopsin expressed in E. coli (occurring at pH 5), the protein-conformation changes of this transition as well as the protonated Schiff base deprotonation may be controlled not by surface pH alone, but rather by the coupling between surface potential and the general protein internal structure around the active site. The results also suggest that Tyr-185 does not deprotonate during the photocycle in purple-membrane bacteriorhodopsin.

Bacteriorhodopsins↗

PubMed1990

Influence of general anaesthesia (thiopental sodium) on progesterone and cortisol levels in pregnant goat serum.

6 pregnant Baladi goats underwent general anaesthesia, using thiopental sodium. Intravenous application of 10-15 mg/kg body weight of thiopental sodium in 2.5% solution produced light anaesthesia for about 20 minutes. The effect of general anaesthesia on progesterone and cortisol levels was studied before and during the application of anaesthesia as well as 1/2, 1, 4, and 24 hours after anaesthesia. Progesterone was determined by RIA and cortisol by competitive protein binding reaction. Decrease in progesterone and rise in cortisol were noticed during and after anaesthesia. 4 of 13 foetuses were aborted 1-2 weeks after the application of anaesthesia. 6 were born dead. 2 died few hours after birth, and 1 stayed alive.

Anesthesia, General↗

PubMed1989

Electron transfer between cytochrome a and copper A in cytochrome c oxidase: a perturbed equilibrium study.

Intramolecular electron transfer in partially reduced cytochrome c oxidase has been studied by the perturbed equilibrium method. We have prepared a three-electron-reduced, CO-inhibited form of the enzyme in which cytochrome a and copper A are partially reduced and in an intramolecular redox equilibrium. When these samples were irradiated with a nitrogen laser (0.6-ns, 1.0-mJ pulses) to photodissociate the bound CO, changes in absorbance at 598 and 830 nm were observed which were consistent with a fast electron transfer from cytochrome a to copper A. The absorbance changes at 598 nm gave an apparent rate of 17,000 +/- 2000 s-1 (1 sigma), at pH 7.0 and 25.5 degrees C. These changes were not observed in either the CO mixed-valence or the CO-inhibited fully reduced forms of the enzyme. The rate was fastest at about pH 8.0, falling off toward both lower and higher pHs. There was a small but clear temperature dependence. The process was also observed in the cytochrome c-cytochrome c oxidase high-affinity complex. The electron equilibration measured between cytochrome a and copper A is far faster than any rate measured or inferred previously for this process.

Animals↗

PubMed1989

Tryptophan fluorescence quenching as a monitor for the protein conformation changes occurring during the photocycle of bacteriorhodopsin under different perturbations.

The rates of the quenching and recovery of tryptophan fluorescence are determined in the microsecond-millisecond time scale during the photocycle of bacteriorhodopsin under different perturbations. The kinetics suggest the presence of two quenching processes, a rapid one (on the time scale of photocycle intermediate L550 formation or faster) and a slow one (slightly slower than the slow component of intermediate M412 formation). The slow quenching process is found to respond to different perturbations in the same manner as the slow component of M412 formation. It has the same activation energy, it is inhibited if metal cations are removed, it is negligible at pH values greater than the pKa of tyrosine, and its rate is slowed down when 75% of the lipids are removed. These results, together with the observed value of the quenching activation energy, suggest that the rates of the tryptophan fluorescence quenching, like those of tyrosinate and M412 formations during the cycle, are all determined by the rates of the protein conformation changes. The pH studies of the slow quenching process show that the maximum quenching probability occurs at neutral pH. A rapid decrease in quenching occurs at lower pH (approximately 3 and approximately 5.5) and higher pH (approximately 9). Two quenching mechanisms involving energy transfer to either retinal or to tyrosinate are considered. Protein conformation changes resulting from a change in the ionization state of amino acids of different pKa values could change the tryptophan-retinal (or tryptophan-tyrosinate) coupling and thus the quenching efficiency.

Bacteriorhodopsins↗

PubMed1989

Interaction of dibucaine.HCl local anesthetics with bacteriorhodopsin in purple membrane: a spectroscopic study.

Several spectroscopic techniques (absorption, emission, transient absorption and differential scanning calorimetry--DSC) were used to investigate the deprotonation of dibucaine.HCl in a hydrophobic environment, and the interaction sites and mechanisms of the local anesthetic dibucaine.HCl on bacteriorhodopsin (bR) in purple membrane. The important results are summarized as follows: (1) the visible absorption features of native (lambda max = 568 nm) and deionized (lambda max = 608 nm) bR are sensitive to the amount of dibucaine.HCl added; (2) the emission spectrum of dibucaine.HCl embedded in the retinal-free mutant bR is similar to that of dibucaine free base in Triton X-100 micellar solutions; (3) the phosphorescence emission of dibucaine at 77 K is completely quenched by bR and the fluorescence quenching rate for the incorporated dibucaine.HCl in bR was determined as kq = 4.09 x 10(13) M-1 s-1; (4) the incorporation of dibucaine.HCl in bR inhibits the slow component rate of formation of M412 and decreases the amount of M412 formation in the photochemical cycle of bR; and (5) the thermal stability of native bR was measured by DSC in the presence and absence of dibucaine and yielded an endothermic transition at 95.9 +/- 1.0 degrees C with 13.6 J/g (3.25 +/- 0.12 cal/g) of enthalpy changes. All observations suggest that the action site of the local anesthetic, dibucaine.HCl, is near or at the chromophore, i.e. the retinal Schiff base of bR. The anesthetic action on bR purple membrane is probably via a specific site binding, but not a conformational mechanism.

Bacteriorhodopsins↗

PubMed1988

Deprotonation of lipid-depleted bacteriorhodopsin.

The removal of 75% of the lipid from bacteriorhodopsin caused the following: (i) decreased efficiency and rate of deprotonation of the protonated Schiff base (as monitored by absorption of the M412 intermediate); (ii) increased efficiency of deprotonation of deionized samples; (iii) a decrease by 1 unit in the pH at which deprotonation ceases; (iv) increased intensity of Eu3+ emission in Eu3+-regenerated deionized delipidated samples; (v) increased exposure of the Eu3+ sites to water; and (vi) elimination of the dependence of the deprotonation efficiency on the metal cation concentration. These results are discussed in terms of changes in the protein conformation upon delipidation, which in turn control the deprotonation mechanism.

Bacteriorhodopsins↗

PubMed1988

Effect of UV-irradiation on some aspects of metabolic activities in Aspergillus flavus and Penicillium notatum.

Near-UV (NUV) irradiation was found to stimulate protein synthesis in Penicillium notatum and Aspergillus flavus. DNA was also induced by short periods of NUV (10 and 20 min) in P. notatum. Synthesis of DNA in A. flavus decreased under the same treatment and then increased when irradiation was for long periods. The reverse of this observation was seen in the case of RNA synthesis, while RNA synthesis was significantly inhibited by NUV in P. notatum. Induction of RNA synthesis was observed in A. flavus. Far-UV (FUV) irradiation induced protein synthesis in P. notatum and A. flavus; the increase was more pronounced in A. flavus. FUV slightly inhibited DNA synthesis in P. notatum, but the synthesis in A. flavus was fairly constant. RNA synthesis was reversed to a certain extent by FUV in both fungi. UV irradiation produced no effect on the process of lipid synthesis. Total soluble carbohydrates were decreased by NUV in P. notatum and increased markedly in A. flavus (240 min NUV). FUV irradiation resulted in an increase in total soluble carbohydrates in both fungi.

Aspergillus flavus↗

PubMed1986

Influence of monensin on fertility in rats.

Monensin was given orally to female rats at two dose levels (1.75 and 3.50 mg/kg body weight) over the period of 9-17 days of pregnancy where organogenesis of fetuses occur. The dams were killed on the nineteenth day of gestation and their fetuses were subjected to morphological, visceral and skeletal examination. The small dose of monensin increased the number of resorbed and dead fetuses and induced marked retardation in growth of viable fetuses, but visceral or skeletal defects in these fetuses were not seen. Large doses produced fetal resorption in all dams and no viable fetuses were delivered. Prolonged oral administration of monensin in male rats for 60 successive days at two dose levels, decreased the conception rate in non-treated females (mated with treated males) to 33.3% and 0% for the small and large doses, respectively. Both doses markedly decreased the weights of testicles, epididymides and seminal vesicles. The small dose of monensin caused oligospermia, whereas the large dose induced azospermia. Both doses decreased the activity of spermatogenic epithelium and caused degeneration in germ cells after histopathological examination of the testicles. It is concluded that monensin given during pregnancy to female rats is fetotoxic and when administered chronically to male rats, causes damage to the reproductive organs. The delayed effects of this drug are especially prominent.

Abnormalities, Drug-Induced↗

PubMed1984

Production of cyanocobalamine by Azotobacter chroococcum.

A strain of Azotobacter chroococcum was found to produce a considerable amount of cyanocobalamine especially when cultivated in a medium enriched with 0.3% ammonium chloride. Maximal production of the vitamin was achieved after six days of incubation in static cultures. The organism required molybdenum, iron (Fe++), cobalt and ascorbic acid for optimal production of cyanocobalamine. The initial supplementation of the medium with cyanocobalamine did not affect the formation of the vitamin. The least concentration of ascorbic acid tested greatly initiated the production of vitamin B12. Higher concentrations were not effective. In the presence of molybdenum, iron, cobalt and ascorbic acid maximal secretions of cyanocobalamine was attained in the presence of 3% sucrose or an amount of hydrolyzed rice-bran containing 2% sugar. Higher concentration of rice-bran was toxic to the organism.

Ammonium Chloride↗

PubMed1974