Protein conformational changes induced by guanidine at predenaturational concentrations

The nature of the molecular event that apomyoglobin undergoes at predenaturational concentrations of guanidine has been investigated by means of steady-state and multifrequency phase and modulation fluorometry. The results have been compared to those observed for liver alcohol dehydrogenase. From these studies has been hypothesized a different susceptibility of the distinct elements of secondary, super-secondary, and tertiary structure towards the denaturing action of guanidine at predenaturational concentrations.     

Glycolipid changes in tissues of wheat leaves induced by exogenous hydrogen peroxide

The results of the study of H2O2 treatment of wheat leaf glycolipid composition are presented. The fraction changes depended upon H2O2 concentration, way of treatment and exposition. The most typical reaction was galactolipid (MGDG, DGDG) content increase while lower sulpholipid variations at low doses of the root treatment and at leaf spraying.     

Functional and conformational changes in the aspartic protease cardosin A induced by TFE

Conformational and functional changes of cardosin A, an aspartic protease of vegetal origin, in the presence of 2,2,2-trifluoroethanol (TFE), were assessed. TFE induced alterations of cardosin activity and conformation that differed with the solvent concentration. MD simulations showed that there are significant local alterations in protein flexibility and TFE molecules were found to replace several hydration molecules in the active site of the enzyme. This may explain some of the activity loss observed in the presence of TFE, especially at low TFE concentrations, as well as the recovery of enzyme activity upon aqueous dilution, indicating the release of the TFE molecules from the active site.     

Functional changes of rat brain mitochondrial enzymes induced by monomeric cholesterol

• 1.1. The binding of [¹⁴C]cholesterol into rat brain mitochondrial membranes follows an exponential path described by the general formula y = a.e^bx. [¹⁴C]cholesterol glucoside binding has a sigmoidal character where the “best-fit” curve of this type of binding is the one described by the Hill equation with Hill coefficient h = 2.06. These findings suggest a positive cooperativity in the binding of both compounds into rat brain mitochondrial membranes.
• 2.2. The specific activity of the outer mitochondrial membrane enzyme monoamine oxidase was linearly decreased at different concentration of cholesterol or its glucoside.
• 3.3. The specific activity of the inner mitochondrial membrane enzyme succinate-cytochrome c reductase was linearly decreased, while that of Rotenone-sensitive NADH-cytochrome c reductase was exponentially increased, at different concentrations of cholesterol.
• 4.4. These results are discussed in terms of specific interactions of cholesterol with constituent mitochondrial membrane lipids and their implications for deviations from normal neuronal function.

     

Functional and morphological changes induced by tunicamycin in dividing and confluent endothelial cells.

Cultured bovine aortic endothelial cells treated with tunicamycin, an inhibitor of glycoprotein synthesis, developed a concentration-dependent inhibition of N-acetylglucosamine-1-phosphate transferase activity, and this inhibition was correlated with a substantial decrease in [3H]mannose incorporation by the cells. Endothelial cells were very sensitive to tunicamycin, and changes in their morphology occurred as a result of the inhibition of glycoprotein synthesis. The cells became elongated, the surface irregular, roughened, and granular, and there was an increase in the interstitial space between the cells. Electron dense material was accumulated within and dilated the rough endoplasmic reticulum, and the distribution of the glycoproteins laminin and fibronectin throughout the endothelial cell monolayer was modified. These morphological changes coincided with functional impairment with the permeability of endothelial cell monolayers to both 125I-albumin and [3H]inulin being increased by treatment with tunicamycin (10(-6) M) for 24 h. These results indicate that the synthesis of glycoproteins is crucial for cell-cell adhesion and the functional properties of the endothelial lining of blood vessels.     

Functional and ultrastructural changes induced by short term ovariectomy on pancreatic islets

The effect of short term ovariectomy and combined estrogen-progesterone treatment on insulin secretion was studied and related to the changes observed in the glucose oxidation, calcium uptake and insulin content, as well as the ultrastructure of pancreatic rat islets. It was found that ovariectomy was followed by an enhanced glucose-induced insulin secretion, glucose oxidation, calcium uptake and insulin content together with striking changes at the ultrastructural level located only in the B cell population. They were represented by the appearance of broad cytoplasmic areas containing an homogeneous fine granular material, enclosing sometimes organelles, B secretory granules with their clear halo significantly enlarged and marked dilation of the rough endoplasmic reticulum. Conversely, in ovariectomized-rats supplemented with estrogen-progesterone, the insulin response as well as the above mentioned metabolic parameters return to normal control values. Although not completely, ultrastructural changes also showed a clear amelioration. On account of our results, we might suggest that insulin secretion is controlled, at least in part, by the circulating levels of estrogen and progesterone throughout their effect on pancreatic islet metabolism. The absence of this control over a short term period produces a reversible increment in B cell function and the appearance of important changes at the ultrastructural level.     

Functional and metabolic changes of guinea pig peritoneal macrophages induced by bacterial vaccines

Phagocytic activity of peritoneal macrophages of guinea pigs injected subcutaneously with bacterial vaccines was found to be increased. The phagocytic index remained unchanged or was decreased. In addition, a decreased candidacidal activity was observed. Metabolic activation of macrophages, measured by the INT test, was inhibited in unstimulated cells while cells stimulated with zymosan or opsonized zymosan exhibited higher values of the INT test as compared with control animals. After injection of vaccines the number of peritoneal macrophages was increased, but the spleen mass decreased. Translated by I. Miler     

Stress and activity correlated changes of hydroxylase cofactor concentrations in brain tissues and blood

A significant inverse correlation between individual hydroxylase cofactor concentration and spontaneous locomotor activity exists in male rat striatum in the light, but not the dark, phase of the diurnal cycle. No relationship exists in the nucleus accumbens. Electric shock stress significantly elevated plasma and hypothalamic cofactor concentration and decreased cofactor concentration in the raphe nuclei without significantly changing it in the striatum and the hippocampus. Alterations of hydroxylase cofactor concentration in brain and blood under stress manipulation may have its functional significance and clinical implications.     

Functional changes of mice Sertoli cells induced by Cr(V)

Transport of macromolecules from the interstitial testis tissue to cells at the adlumenal compartment of the seminiferous epithelium occurs naturally through Sertoli cells. In previous studies we have shown that Cr(V) intoxication disturbed spermatogenesis in mice. To test if Sertoli cells are affected by chromium, a well proved carcinogen, the uptake and the horseradish peroxidase transport ability of isolated seminiferous tubules of mice administered with a chromium(V) compound, have been studied. Male CD-R mice were exposed daily for 5 days to [Cr^V-BT]^2– through subcutaneous injection and comparisons were made with groups of vehicle-treated mice. Using an in vitro assay we demonstrated that the seminiferous tubules were able to uptake and transport the tracer, in a much faster way than controls, mainly via intercellular and transcellular pathways, providing evidence that this functional role of Sertoli cells is affected by the Cr(V) compound. These findings might improve the knowledge on the toxicity mechanisms of chromium.     

Ultrastructural changes induced by low concentrations of DDT in the livers of the zebrafish and the guppy

Following exposure to 0.3–3.0 ppb DDT, the livers of zebrafish and guppies were examined by electron microscopy. After 24 h in 1.0 ppb or 72 h in 0.3 ppb, zebrafish had a complete loss of glycogen, decrease in cell size and a cytoplasmic compartment filled with rough endoplasmic reticulum (ER). Guppies exposed for periods of up to 28 days showed only a gradual accumulation of smooth ER and no change in glycogen, lipid, rough ER or cell size. The relationship of these changes to the zebrafish's sensitivity and the guppy's tolerance to DDT is dicussed.     

Precipitation membranes: III. Reversible changes of membrane properties induced by alterations in ionic concentrations

Summary The conditioned state of a precipitation membrane with its particular properties exists within a limited range of membrane potentials and requires certain minimum concentrations,C _lim, of the generating ions in the adjoining solutions. We investigated these quantities for the BaSO₄ cellophane membrane and foundC _lim to be 10×10^–5 n (0.5×10^–4 m), equally for Ba⁺⁺ and SO ₄ ^–– . Beyond these limits, the membrane becomes deconditioned. This transformation is a reversible process provided the limits have not been surpassed too far. The capability for de- and reconditioning is a characteristic and unique property of precipitation membranes, not found in other membrane systems. The phenomenon is explained by the adsorption theory for precipitation membranes. It allows wide modifications and quick variations of the electrical properties and permeability of the membrane in an easy and reversible manner.