Search PubMed⌕ Search

Biomedical subjects

D Cooper

Publications and source records attributed to D Cooper.

At least 253 records · Page 14Linked to original sources
PubMed1976

Reversible restrictive lung disease stimulating asthma.

A young adult woman presented with spontaneous and exercise-induced episodic dyspnea without wheezing. During dyspneic episodes all static lung volumes decreased markedly, the inspiratory capacity fell from 3.0 to 1.1 litres and total lung capacity from 5.3 to 2.6 litres. Airway resistance (Raw) remained normal, and maximal expiratory flows at low absolute lung volume actually increased. Static compliance decreased from 0.153 to 0.077 litre/cmH2O, and the elastic recoil increased from 2.8 to 4.8 cmH2O at 50% of baseline total lung capacity when dyspneic. Upstream airway resistance (Rus) remained unchanged, 1.7 cmH2O/litre/sec. All physiologic variables indicated a reversible restrictive process exists, the origin of which is unclear. It is concluded that the episodic increase in elastic recoil properties results in [1] loss of volume primarily in the alveolar ducts and sacs, [2] preservation of normal Rus by an increase in driving pressure, and [3] maintenance of normal Raw by stabilization of larger airways.

Adult↗
PubMed1975

Cellulose synthesis by Acetobacter xylinum. I. Low molecular weight compounds present in the region of synthesis.

An analysis has been made of the low molecular weight fraction present in the region of cellulose synthesis in Acetobacter xylinum suspensions. A number of nucleic acid bases, nucleosides and nucleotides, together with alpha-glucose 1-phosphate and UDPG, were detected in various extracts of washed cells supplied with glucose. Since glucose-6-P could be detected in extracts of ultrasonically disrupted cells, but not in extracts of whole cells, it was concluded that separate pools of hexose phosphate exist in A. xylinum. Preferential release of alpha-glucose-1-P, UDPG and nucleotides was observed during ethanol and EDTA treatment of bacteria. Electron microscopic examination of treated and untreated cells revealed that extensive modification of the cell wall region occurred during such treatments. The results support the proposal that alpha-glucose-1-P, UDPG and nucleotide pools are localised in the cell envelope region, possibly in the periplasm, and that A. xylinum possesses a second permeability barrier outside the cytoplasmic membrane. Nucleic acid bases and nucleosides were observed to diffuse freely through the cell wall and accumulate in the medium, probably as the result of nucleic acid breakdown. The results imply that the effects of cell damage caused by the isolation of the bacteria from the surface pellicle of the culture medium, together with nutrient deprivation, should be considered in work using the non-proliferating system. A stydy of the variation in concentration with time of alpha-glucose-1-P and UDPG, during cellulose synthesis, indicated that both components may play an immediate role in cellulose synthesis. Glycosylated lipid compounds were detected in both cell wall extracts and supernatant fluid, but it is not certain whether these compounds are constituents of the supernatant fluid in vivo.

Cellulose↗
PubMed1975

Cellulose synthesis by Acetobacter xylinum. II. Investigation into the relation between cellulose synthesis and cell envelope components.

Cell envelope fractions, capable of cellulose synthesis from uridine diphosphate glucose, alpha-glucose-1-phosphate, glucose-6-phosphate and glucose, have been isolated from Acetobacter xylinum suspensions and various enzymatic properties examined. Essential enzymes were found to be distributed throughout the cell envelope region, with both inner (cytoplasmic) and outer (cell wall) membranes contributing to cellulose synthesis. The central role of UDPG in cellulose synthesis was confirmed and the results indicated that the nucleoside diphosphate sugar functions solely in the cell envelope region of whole cells. A comparison of properties of the cell envelope system with those of different preparations used by other workers, suggested that the method of cell disruption may influence substrate specificity.

Cell Membrane↗
PubMed1975

Cellulose synthesis by Acetobacter xylinum. III. Matrix, primer and lipid requirements and heat stability of the cellulose-forming enzymes.

The addition of soluble cellodextrins of increasing size to a cell envelope preparation of Acetobacter xylinum stimulated cellulose synthesis from UDPG. This stimulation was attributed to both acceptor and activator effects. Enzymes required for cellulose synthesis were found to be heat-unstable and those required for synthesis of glycosylated lipid components from UDPG, heat-stable. Both heat-inactivated envelope fragments and supernatant fluid from whole cells were necessary for cellulose synthesis from UDPG. Cellulose was not formed from UDPG in the presence of either supernatant fluid alone or heat-inactivated envelopes alone. The combined results of this and previous studies suggest that either the cell envelope is necessary for synthesis of a more immediate precursor to cellulose than UDPG, or that the synthesis from UDPG requires a matrix. The former suggestion and its possible link with lipid intermediate involvement was strengthened by the observation of inefficient glycosylated lipid formation by a celluloseless mutant strain of A. xylinum. The possible locations of various enzyme activities required for the synthesis of the cellulose precursor are indicated and a possible microfibril nucleation process is discussed.

Cell Wall↗