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Biomedical subjects

A K Ahmed

Publications and source records attributed to A K Ahmed.

15 recordsLinked to original sources
PubMed1992

Isospora solimanae sp. nov. from the Egyptian hoopoe (Upupa epops major).

Isospora solimanae (sp. nov.) is recorded for the first time infecting the Egyptian hoopoe (Upupa epops major). Unsporulated as well as sporulated oocysts were studied, photographed and compared with other isosporan infections of related birds. Site of infection and invasion limits were determined among naturally infected hoopoes and represented diagramatically. The rate of infection was congruent to 37.5%, and its severity considered to be non-pathogenic, since no remarkable lesions were observed. No extra-intestinal site of parasite development was recorded.

Animals↗
PubMed1992

Studies on Eimeria species naturally infecting Gerbillus pyramidum (1) Exogenous stages.

Exogenous stages of two new Eimerian species, naturally infecting the Egyptian gerbil Gerbillus pyramidum were described and diagnosed in the present study. (1) The subspherical type of oocysts was 20 x 17 microns (length x width) in average. These are colourless and enveloped within an even double-layered oocyst wall. Sporulated oocysts containing four sporocysts each averaged in 10 x 8 microns, and a small spherical oocyst residual body was also observed. This type is termed Eimeria pyramidi after the species name of its host. (2) The second type of oocysts was elongated in shape measured congruent to 21 x 16 microns. These are colourless and enclosed within smooth double layered oocyst wall. Sporulated oocysts of this type were lacking oocyst residual bodies. This type is termed Eimeria gerbilli after the generic name of its host. Both types of described oocysts lack micropyle and polar cap.

Animals↗
PubMed1992

Fine structure studies of microgametogenesis of Eimeria adenoeides (Eimeriidae, Sporozoa) infecting turkeys in Egypt.

The Ultrastructure of microgametogenesis of Eimeria adenoeides was studied in the intestinal epithelium of experimentally infected turkeys' Meleagris gallopavo gallopavo. Microgamonts were recognizable by the presence of peripherally arranged nuclei and the presence of two centrioles between each nucleus and the limiting membrane of the gamont. A nuclear spindle apparatus and an intranuclear centrocone directed toward the centriole were observed. Each young microgamont was surrounded by a very narrow parasitophorous vacuole which widened during development and contained a few intravacuolar folds. Differentiation of the microgamete began when elevations of the limiting membrane appeared above the centrioles. This event was accompanied by the segregation of nuclear content into a dense osmiophilic portion and an electron-pale portion. A gradual protrusion of the dense portion of the nucleus and developing flagella into the parasitophorous vacuole was proceeded. Microgametes had an anterior perforatorium, a dense elongate nucleus, with an anteriorly positioned mitochondrion in a small groove of the nucleus. Usually two flagella could be detected per each mature microgamete.

Animals↗
PubMed1991

Electron microscopic study on macrogametogenesis of Eimeria labbeana infecting the Egyptian wild doves and host-parasite relationship.

The development of macrogametes of Eimeria labbeana was studied by electron microscopy in the epithelial cells of the villi at 96 hrs. post-infection. Appearance of young macrogamonts was characterized by the loss of the architecture of the apicomplexa (polar ring, rhoptries, micronemes, conoid, subpellicular microtubules), while the pellicle became only one unit membrane. This was associated by the formation of wall forming bodies II then I. Moreover, the mitochondria, endoplasmic reticulum and Golgi were increased in the cytoplasm. Amylopectin granules as well as lipid globules were greatly increased in mature macrogametes. Host cell reaction due to infection included enlargement and deformation of infected cells, hypertrophy of their nuclei, swollen and degeneration of mitochondria, endoplasmic reticulum and vacuolation of ground cytoplasm. These changes occur in both cells with and without parasite.

Animals↗
PubMed1977

Protein thiol-disulfide interchange and interfacing with biological systems.

Disulfide-containing proteins offer unique advantages for mechanistic studies of the formation of native three-dimensional structure from unordered, reduced precursors. The main advantage is that covalent intermediates are formed; by characterizing these intermediates, one obtains substantial information about the reaction pathway. Thiol-disulfide interchange is a major component of most oxidative mechanisms carrying thiol to disulfide; thus, it required some attention in its own right. Afinsen's descriptions of a "shuffle-ase" enzyme led us to examine the rates of the uncatalyzed exchange under physiologically plausible conditions. Somewhat surprisingly, we found that the rates for formation of several native proteins in uncatalyzed systems containing GSSG and GSH are as great as with the "shuffle-ase" enzyme, suggesting that a substantial portion of biological thiol oxidations proceed by uncatalyzed exchange. While thiol-disulfide exchange of course results in no net change in the oxidation level of a system, catalytic linkage of thiol or disulfide to other redox systems provides a mechanism for achieving net changes.

Chemical Phenomena↗
PubMed1977

Semimicro-titrimetric method for the determination of activity-concentration of heparin.

A semimicro-titrimetric method for the determination of heparin is developed. The method depends upon the determination of the sulphate content of the acid drolysate of heparin by adding an excess of barium chloride and back titration with standard sulphuric acid, using sodium rhodizonate as indicator. The method measures the biological activity of 10-50 mg of heparin, with a mean accuracy (p = 0.05) 99.73 +/-0.81%. Application of the proposed method for the determination of heparin in some pharmaceutical preparations is carried out by precipitation of the intact heparin molecule with cetyltrimethylammonium bromide, ashing of the precipitate and determination of its sulphate content; alkaline and acid degradation products do not interfere with the proposed procedure.

Blood Coagulation↗
PubMed1975

Salt effects in the glutathione-facilitated reactivation of reduced bovine pancreatic ribonuclease.

The rate of regeneration of reduced RNase by glutathione was examined in the presence of several added substances: substrate, phospholipid, other proteins, bacterial ribosomes, and neutral salts. Of these, only neutral salts showed substantial effects. K2HOP4 and (NH4)2SO4 strongly accelerated regeneration, the alkali chlorides showed moderate acceleration or inhibition, while LiBr and KSCN strongly inhibited. The t1/2 for regeneration in 1 M Pi is 4 min compared to 75 min in the absence of Pi; in 0.5 M KSCN t1/2 greater than 100 min. The pattern of specific salt effects is similar to a Hofmeister series. There is a strong parallel between the pattern of specific salt effects on the kinetics of RNase regeneration and the pattern of effects of the same salts on the equilibrium stability of biopolymers. This suggests that the role of salts in the regeneration is to stabilize or destabilize rate-limiting folding intermediates. Pi-accelerated glutathione regenerations showed a broad temperature optimum from 30-37 degrees. In strong contrast with the virtual concentration independence of the Pi-free controls, with Pi = 1 M, both rates and yields of RNase activity were decreased markedly at [RNase] greater than 2 x 10(-6) M. Phosphate and pyrophosphate showed additive, and in some cases, synergistic accelerations. These results suggest that specific ion binding occurs in addition to general solvent effects.

Animals↗
PubMed1975

Nonenzymic reactivation of reduced bovine pancreatic ribonuclease by air oxidation and by glutathione oxidoreduction buffers.

With the glutathione system that leads to rapid regeneration of reduced lysozyme (Saxena, V. P., and Wetlaufer, D. B. (1971) Biochemistry 9, 5015), reduced pancreatic ribonuclease (RNase) regenerated activity in high yield (greater than 90%) but at a considerably lower rate (t1/2 approximately 75 min). Systematic examination of the effects upon regeneration of the concentrations and ratios of reduced and oxidized glutathione (GSH and GSSG) showed the same broad optima for RNase as were earlier found for lysozyme: [GSSG] = 5 X 10(-4) M, [GSH] = 5 X 10(-3) M. Regeneration of reduced RNase by air oxidation was shown to be inhibitable by 10(-4) M EDTA, whereas the glutathione regeneration was unaffected by EDTA. In addition the air-oxidative regeneration showed a strong temperature dependence, in contrast with the glutathione system. The mechanisms of these two kinds of regenerations are therefore different. Six potentially catalytic metal ions were tested in the air-oxidative regeneration of RNase: Cu2+, Co2+, Mn2+, Fe3+, Zn2+, and Ni2+. Of these, only Cu2+ enhanced the rate of regeneration of RNase activity, although both Cu2+ and Co2+ catalyzed thioloxidation of reduced RNase. The rates and yields of RNase regenerations were independent of protein concentration from 3 X 10(-7) M to 1.2 X 10(-5) M in the glutathione system. Preincubation of freshly dissolved reduced RNase under nonoxidizing conditions before adding glutathione did not change the rate or extent of regeneration. Studies of its pH dependence showed that the glutathione regeneration depends on the deprotonation of prototropic groups with 7.5 less than pK less than 8.0. The major ion exchange chromatographic peaks from glutathione and air-oxidative regenerations appeared to be identical with native RNase, by the criteria of specific activity, chromatographic mobility, and circular dichroic spectra. The glutathione system permits regeneration at much higher RNase concentration than the air regeneration, with rates and yields comparable to the greatest reported for air regeneration.

Animals↗