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Biomedical subjects

M Silver

Publications and source records attributed to M Silver.

At least 37 records · Page 2Linked to original sources
PubMed1977

Ferrous iron oxidation and uranium extraction by Thiobacillus ferrooxidans.

The microbiological oxidation of ferrous iron in batch and continuous systems has been investigated in relation to uranium extraction from a low-grade ore by Thiobacillus ferrooxidans. The influence of the parameters, agitation, and aeration on oxygen saturation concentration, rate of oxygen mass transfer, and rate of ferrous iron oxidation was demonstrated. The kinetic values, Vmax and K were determined using an adapted Monod equation for different dilution rates and initial concentrations of ferrous iron. The power requirements for initial leaching conditions were also calculated. Uranium extraction as high as 68% has been realized during nine days of treatment. Regrinding the leach residue and its subsequent leaching yielded 87% uranium solubilization.

Ferrous Compounds↗
PubMed1977

The effects of bilateral adrenalectomy or hypophysectomy of the foetal lamb in utero.

1. Foetal hypophysectomy or bilateral adrenalectomy, carried out in utero at about 100 or 125 days gestation respectively, increased the length of gestation in sheep. It was confirmed that pregnancy was not prolonged significantly if hypophysectomy or adrenalectomy was carried out on one of a pair of twins. The hypophysectomized foetus was, however, smaller and the adrenalectomized foetus larger, than the unoperated twin. 2. In about half of the previously operated foetuses intravascular catheters were inserted into both mother and foetus, either at about 125 days, for a comparison with normal catheterized foetuses, or during the post-mature period. Both adrenalectomized and hypophysectomized foetuses appeared to have little resistance to stress or infection and the majority survived only 1-2 weeks after the insertion of catheters. 3. Maternal peripheral plasma oestrogen, progesterone and corticosteroid concentrations did not appear to be altered by either foetal hypophysectomy or adrenalectomy and were maintained in the normal range during prolonged gestation. 4. Foetal plasma oestrogen concentrations were significantly lower after hypophysectomy or adrenalectomy than values found in control lambs. Plasma progesterone values were low in all three groups of foetuses. 5. Plasma corticosteroid concentrations after foetal hypophysectomy (12-6 ng/ml.) or adrenalectomy (14-7 ng/ml.) were in the same range as the values for control lambs before the pre-partum rise (14-6 ng/ml.). However, there was a small but significant maternal-to-foetal plasma corticosteroid gradient in the two operated groups whereas this difference was not found in the control animals. 6. Tissue glycogen concentrations were measured in non-catheterized adrenalectomized and hypophysectomized foetuses. In these two groups, whether examined before 149 days or after prolonged gestation, liver glycogen concentrations were 30-40% of those in non-catheterized control foetuses at term. In other respects there was little apparent difference between adrenalectomized and control foetuses. 7. Hypophysectomized foetuses had significantly higher glycogen concentrations in heart, skeletal muscle and lung compared with control or adrenalectomized lambs. Plasma glucose and fructose values were also low in this group compared with control foetuses.

Adrenal Cortex Hormones↗
PubMed1976

Microbiological leaching of a chalcopyrite concentrate by Thiobacillus ferrooxidans.

The microbiological leaching of a chalcopyrite concentrate has been investigated using a pure strain of Thiobacillus ferrooxidans. The optimum leaching conditions regarding pH, temperature, and pulp density were found to be 2.3, 35 degrees C, and 22% respectively. The energy of activation was calculated to be 16.7 kcal/mol. During these experiments the maximum rate of copper dissolution was about 215 mg/liters/hr and the final copper concentration was as high as 55 g/liter. This latter value is in the range of copper concentrations which may be used for direct electrorecovery of copper. Jarosite formation was observed during the leaching of the chalcopyrite concentrate. When the leach residue was reground to expose new substrate surface, subsequent leaching resulted in copper extractions up to about 80%. On the basis of this experimental work, a flow sheet has been proposed for commercial scale biohydrometallurgical treatment of high-grade chalcopyrite materials.

Biodegradation, Environmental↗
PubMed1976

Rhodanese from Thiobacillus A2: catalysis of reactions of thiosulphate with dihydrolipoate and dihydrolipoamide.

Rhodanese (thiosulphate:cyanide sulphurtransferase EC.2.8.1.1) was purified 25- to 30-fold from thiosulphate-grown Thiobacillus A2. It exhibited a pH optimum between pH 10-2 and 10-4 and apparent Km values of 0-36 mM-Na2S2O3 and 17 mM-KCN. Ultraviolet spectrophotometry and thin-layer chromatography showed that the enzyme catalysed the reaction of S2O3(2-) with dihydrolipoic acid or dihydrolipoamide, producing alpha-lipoate or lipoamide, with the intermediate production of the persulphides of dihydrolipoate and dihydrolipoamide, which were demonstrated chromatographically. This is the first demonstration of catalysis by a thiobacillus rhodanese of reactions which are likely to be physiologically important in the oxidative dissimilation of thiosulphate by a central energy-conserving pathway.

Amides↗
PubMed1976

Some aspects of foetal and uteroplacental metabolism in cows with indwelling umbilical and uterine vascular catheters.

1. The experiments were carried out on conscious pregnant Jersey cows with intravascular catheters implanted during late gestation in umbilical and uterine vessels. All but three of fifteen animals delivered live healthy calves. 2. Rountine daily analyses were made of blood gas tensions, pH and packed cell volume in foetal and maternal blood; plasma concentrations of glucose, fructose, lactate and urea were also determined. Measurements of plasma free fatty acids and blood acetate concentrations were made less frequently. Foetal heart rate and arterial blood pressure were recorded in animals with an umbilical arterial catheter. 3. The concentration differences between foetal and maternal blood or plasma in glucose, urea and acetate were measured in fifteen animals. The maternal-to-foetal glucose and acetate gradients across the placenta were high while the foetal-to-maternal plasma urea differences were small. 4. In those animals with patent arterial and venous catheters, uterine and umbilical blood flows were measured together with the arteriovenous differences in 02, glucose, acetate and lactate so that rates of foetal and uterine consumption could be estimated. The rates of utilization of O2, glucose and acetate by the foetus were lower than the values for the whole uterus, while the uteroplacental metabolism of these substrates was very high. 5. Significant amounts of lactate, which appeared to be produced by the uteroplacental tissue, were utilized by the foetus; the remainder passed into the uterine venous blood. 6. The total substrate/O2 quotient for the foetus, calculated from the utilization of known metabolites, appeared to be greater than 1. Thus, in the calf some carbon accumulation from sources other than amino acids, the uptake of which was not measured, would seem to occur. These results and the metabolic activity of the uterine tissues are discussed in relation to comparable findings in the sheep.

Acetates↗
PubMed1976

Adrenal and pancreatic endocrine responses to hypoxia in the conscious calf.

1. Pancreatic and adrenal responses to intense hypoxia have been examined in conscious unrestrained calves 3-5 weeks after birth. 2. The outputs of both cortisol and corticosterone from the right adrenal gland rose steadily in response to hypoxia and this cortical secretory response was accompanied by a pronounced increase in blood flow through the gland. The changes in both steroid output and adrenal blood flow corresponded with those which occur in response to supramaximal doses of corticotrophin in calves of the same age. 3. Neither adrenaline nor noradrenaline were released in significant amounts from the adrenal medulla until the arterial PO2 had fallen below 15 mmHg. Such severe hypoxia caused secretion of catecholamines at rates comparable with those recorded during maximal stimulation of the sympathetic innervation to the gland in anaesthetized calves. The response to intense hypoxia in these conscious calves differed from that which occurs under anaesthesia in that the amount of adrenaline released was invariably greater than that of noradrenaline. 4. Severe hypoxia produced a rapid but transient increase in plasma glucagon concentration, followed by a pronounced rise in plasma glucose concentration in animals with abundant liver glycogen. No change in plasma insulin concentration was observed during hypoxia although it rose subsequently in response to hyperglycaemia. 5. Bilateral section of the splanchnic nerves virtually abolished the release of catecholamines in response to hypoxia but the adrenal cortical and pancreatic responses did not appear to be affected.

Adrenal Glands↗
PubMed1976

Microbiological oxidation of synthetic chalcocite and covellite by Thiobacillus ferrooxidans.

The microbiological oxidation of synthetic chalcocite and covellite has been investigated using an adapted strain of Thiobacillus ferrooxidans. Biodegradation of chalcocite was found to be 90 to 100% and that of covellite 45 to 60%. Optimum conditions for the oxidation of chalcocite were: pH, 1.7 to 2.3; temperature, 35 C; and ferric iron concentration in the range of 0.004 to 0.01 M. For covellite, the optimum conditions were: pH 2.3; temperature, 35 C; and ferric iron concentration in the range of 0.004 to 0.02 M. The energies of activation were determined to be 16.3 kcal (ca. 6.8 X 10(4) J) per mol and 11.7 kcal (ca. 4.8 X 10(4) J) per mol for chalcocite and covellite, respectively.

Biodegradation, Environmental↗