Search PubMed⌕ Search

Biomedical subjects

A C Dean

Publications and source records attributed to A C Dean.

At least 19 recordsLinked to original sources
PubMed1990

Trimethyl lead degradation by free and immobilized cells of an Arthrobacter sp. and by the wood decay fungus Phaeolus schweinitzii.

The continuing production of leaded petrol generates liquid wastes containing recalcitrant trialkyl lead, for which no suitable chemical treatment has been formulated. This investigation explores the feasibility of using microorganisms to catalyse the rate-limiting step of trimethyl lead degradation to dialkyl lead; this disproportionates chemically to give, ultimately, Pb2+ which is treatable by classical methods. An Arthrobacter sp. and a wood decay macrofungus, Phaeolus schweinitzii provide novel evidence for metabolic trimethyl lead (Me3Pb+) degradation. The retention of this activity in immobilized cell column reactors challenged with Me3Pb(+)-supplemented flows suggests that a future biotreatment process may be possible.

Arthrobacter↗
PubMed1984

Cadmium accumulation by a Citrobacter sp.

Cadmium accumulation by a Citrobacter sp. growing in the presence of the metal occurred as a sharp peak during the mid-exponential phase of growth, but cultures showed considerable inhibition of growth compared to cadmium-free controls. This problem was overcome by pregrowing the cells in cadmium-free medium and subsequently exposing them to the metal in the resting state, under which conditions higher concentrations of cadmium were tolerated and metal uptake was enhanced. This ability was retained when the cells were immobilized and then challenged with a flow containing Cd2+; 65% of the metal presented was removed from solution. The influence on uptake of the composition of the exposure buffer and of various cell treatments were investigated and the results are discussed with respect to the anticipated speciation of the cadmium presented to the cells and also with respect to the probable mechanism of metal uptake. This is thought to occur through the activity of a cell-bound phosphatase, induced during pre-growth by the provision of glycerol 2-phosphate as sole phosphorus source. Continued enzyme function in resting cells would then precipitate the metal as cell-bound cadmium phosphate.

Cadmium↗
PubMed1981

Laparoscopy and radioisotope imaging in the investigation of suspected liver disease.

We have reviewed the clinical and investigative details of 141 patients who underwent laparoscopy in order to determine how best this technique can be used. The clinical history and biochemical investigations usually only indicated some form of hepatobiliary disease, but all patients with spider telangiectasia, splenomegaly, or esophagogastric varices had diffuse parenchymal liver disease, and further investigation was only required to detect its cause. Laparoscopy succeeded in 129 patients (91%), and serious complications occurred in six (4%). The appearance of the liver did not accurately reflect the underlying pathology, indicating the need for biopsy in all cases. Laparoscopy and 99mTc-sulfur colloid liver imaging each failed to detect a few hepatic malignancies, but none were missed by both investigations combined, and similar results were obtained for parenchymal liver disease. Scanning and laparoscopy proved a highly accurate diagnostic combination.

Humans↗
PubMed1979

Cadmium and zinc sensitivity and tolerance in Bacillus subtilis subsp. niger and in a Pseudomonas sp.

The action of Cd2+ and Zn2+ on Bacillus subtilis subsp. niger ATCC 9372, and on a Pseudomonas sp. (possibly Pseudomonas fluorescens), isolated from cadmium-polluted soil has been determined and compared with results obtained previously with Klebsiella aerogenes. In liquid medium the lag and the mean generation time of Bacillus subtilis subsp, niger increased with increasing Cd2+ or Zn2+ concentrations whereas only the total biomass of the Pseudomonas sp. was affected. Nevertheless, the responses of both species indicated a specific action at low concentrations and a more general toxic action at high concentrations. The survival on Cd2+ - or Zn2+ - agar depended on the state of the metal ions with regard to chelating ligands and on the nutritional stage of the organisms. In admixture, the metal ions acted synergistically, particularly on the Pseudomonas sp. Resistance to both metal ions developed. It was graded to the training concentration and reciprocal cross-resistance occurred with Bacillus subtilis. subsp. niger but not with the Pseudomonas sp.

Bacillus subtilis↗
PubMed1978

Free sugars in foods.

The values for the free sugars analysed in the samples collected for the fourth edition of McCance and Widdowson's 'The composition of foods' have been combined with values from the literature to provide some basic information on the distribution of free sugars in a range of foods.

Dairy Products↗
PubMed1977

Hexokinase and glucose-phosphoenolpyruvate phosphotransferase synthesis in Klebsiella aerogenes strains growing in continuous culture.

Considerable differences in steady-state hexokinase specific activity were found in 16 N.C.I.B. strains of Klebsiella aerogenes grown in identical conditions in glucose-limited chemostats. Strains of N.C.I.B. 8258 had no detectable activity, but its glucose-phosphoenolpyruvate phosphotransferase specific activity and that of the other strains were closely similar, and it is concluded that this phosphotransferase activity regulates the overall utilization of glucose, in which hexokinase plays no essential role. The hexokinase activity was subject to regulation by the availability of phosphorus, but this did not affect the glucose phosphotransferase activity. tlactose-grown organisms (including strain N.C.I.B. 8258) had no glucose phosphotransferase activity, but more than adequate hexokinase activity to phosphorylate the intracellularly liberated glucose.

Glucose↗
PubMed1976

Action of stannous and stannic chlorides on bacteria.

Stannous or stannic chlorides reduced the growth rate of K. aerogenes, Ps. reptilovora and an unidentified bacterium in a minimal liquid medium and on agar plates. The greatest effect was observed with K. aerogenes and was accompanied by a decreased viability, but 100% survival occurred with other strains. The metal was loosely bound to the cells and there was no direct correlation between the amount adsorbed and the biological response.

Bacteria↗
PubMed1976

Enzymic activities of cadmium- and zinc-tolerant strains of Klebsiella (Aerobacter) aerogenes growing in glucose-limited chemostats.

The activities of phosphatases and some enzymes of glucose metabolism were determined in K. aerogenes NCIB 418 and in two strains derived from it, resistant to 50 mug Cd2+ ml-1 and 16 mug Zn2+ ml-1 respectively, during growth at D = 0.38 h-1 in medium containing beta-glycerophosphate as sole phosphorus source and supplemented with Cd2+ and Zn2+, as appropriate, for the resistant strains. The pH-activity profiles of the phosphatases differed from strain to strain but all showed maximum activity at an acid pH and this activity was very much lower in the Zn2+-resistant strain than in the control and even lower in the Cd2+-resistant strain. Resistance to either metal was associated with decreased glucose-6-phosphate dehydrogenase activity and increased phosphoglucose isomerase activity, suggesting an increased flow of carbon through the Embden-Meyerhof pathway relative to the pentose phosphate pathway, but the efficiency of the conversion of glucose into biomass was largely unaffected. Glucose phosphoenolpyruvate phosphotransferase activity was also lower in the resistant strains.

Acid Phosphatase↗
PubMed1976

Cadmium and zinc sensitivity and tolerance in Klebsiella (Aerobacter) aerogenes.

The resistance of strains of K. aerogenes NCIB 418 'trained' to Cd2+ or Zn2+ in liquid medium is graded to the training concentration. Training to Cd2+ increased the sensitivity to Zn2+ but training to Zn2+ reduced the sensitivity to Cd2+. The trained organisms, particularly those trained to Cd2+, grow slowly in medium containing the metals and the growth rates after 20 and 200 subcultures were not significantly different. The survival of untrained organisms on Cd2+-agar decreased progressively as the Cd2+ concentration was increased, but a threshold concentration of Zn2+ was necessary before any decrease set in. Very low concentrations of Zn2+ potentiated the lethal action of Cd2+ and vice versa, whereas chelating the metal ions with citrate, aspartate or gluconate eliminated it. Nutrient-limitation, as might occur in natural environments, also had a profound effect. Mg2+-limited organisms were particularly resistant to both metals whereas glucose-, NH+4 and PO3-4-limited organisms were very sensitive to Cd2+, and glucose- and K+-limited organisms to Zn2+.

Adaptation, Physiological↗
PubMed1975

Insulinoma.

Explore the source record for details and available documents.

Adenoma, Islet Cell↗
PubMed1974

Pullulanase synthesis in klebsiella (aerobacter) aerogenes strains growing in continuous culture.

1. Pullulanase synthesis was studied in 16 classified (N.C.I.B.) strains and in an industrial strain (R) of Klebsiella aerogenes grown in chemostats containing maltose as inducer and sole carbon source. 2. Maximum synthesis was associated with carbon-limited growth at a low dilution rate (about 0.2h(-1)). The enzyme remained firmly cell-bound and seemed to be located on the cell surface. 3. Three strains had high activity (R, N.C.I.B. 5938, 8017), twelve were intermediate, and two (N.C.I.B. 8153, 9146) had negligible activity but were inducible with pullulan. 4. Pullulan similarly induced low, but adequate, activity in the other strains in conditions (nutrient limitation other than carbon-limitation) in which pullulanase was otherwise very seriously repressed. Nevertheless, in carbon limitation pullulan induced no more enzyme than did maltose, maltotriose or oligosaccharide mixtures, and ;hyperactivity' never developed on protracted culture. 5. Cyclic AMP relieved the transient repression produced by adding glucose to maltose-limited cultures and a further change to glucose-limited conditions led to constitutive pullulanase synthesis. 6. Amylomaltase and alpha-glucosidase activities were also examined but in less detail. 7. The presence of pullulanase in maltose-limited growth is discussed, but no clear function can be assigned to it at present. The molar growth yields for all the strains were very similar, and no correlation was found between the overgrowth of one strain by another and pullulanase activity. Further, any function as a general branching enzyme in polysaccharide synthesis seems unlikely.

Culture Media↗