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Biomedical subjects

W D Stewart

Publications and source records attributed to W D Stewart.

At least 37 records · Page 2Linked to original sources
PubMed1981

Molecular heterogeneity of ferredoxin:NADP+ oxidoreductase from the cyanobacterium Anabaena cylindrica.

The enzyme ferredoxin:NADP+ oxidoreductase (EC 1.18.1.2) from whole filaments of Anabaena cylindrica can be separated into four major fractions by chromatography on phosphocellulose; chromatography using ferredoxin-Sepharose 4B proved to be less satisfactory in separating the fractions. The purified fractions, designated 1, 2, 3 and 4, all showed diaphorase and ferredoxin-dependent cytochrome c reductase activity. The major fractions present were 2 and 3 which were each obtained in an electrophoretically homogeneous state (forms 2 and 3) and represented 30-37% and 30-42%, respectively, of the total enzyme activity. Each was a monomeric species with a molecular weight of approx. 33 000 as determined by gel filtration and sodium dodecyl (SDS)-polyacrylamide gel electrophoresis. Evidence for the presence of a 70 000 molecular weight dimer was also obtained. Forms 2 and 3 had isoelectric points of 5.75 and 6.0, respectively, had similar kinetic properties and were flavoproteins. Extracts of isolated heterocysts showed no form 2 or 3 activity but contained a single form which closely resembled one of the species present in fraction 4; fraction 1 may have been a purification artifact because it was not detected in crude extracts of the cyanobacterium.

Cyanobacteria↗
PubMed1981

Nitrogenase activity and membrane electrogenesis in the cyanobacterium Anabaena variabilis Kütz.

Relationships between nitrogenase activity and individual components of the proton electrochemical potential gradient (delta microH+) in Anabaena variabilis have been investigated. The ionophore nigericin was found to collapse delta pH in favour of the membrane potential (delta psi); hyperpolarization of delta psi was correlated with an increase in nitrogenase activity. A positive relationship between nitrogenase activity and membrane potential was also observed using the ionophore valinomycin and the uncoupler carbonylcyanide m-chlorophenylhydrazone. Furthermore, using the energy transfer inhibitor N,N'-dicyclohexylcarbodiimide, nitrogenase activity appeared to be limited by the supply of reductant rather than ATP. The data suggest, for intact filaments and isolated heterocysts, that delta psi may be important in regulating nitrogenase activity in vivo.

Cell Membrane↗
PubMed1980

A case of Ehlers-Danlos syndrome (type IV) with persisting vitelline duct cyst.

A twenty-four year old white man with Ehlers-Danlos syndrome (Type IV) is presented herein. He demonstrates, or has demonstrated, spontaneous bowel perforation, club feet, cryptorchidism, spontaneous vascular rupture, prominent veins, and distal joint hypermobility. In addition, laparotomy for an acute abdominal condition at four years of age revealed a persisting and gangrenous vitelline duct cyst. We believe this is the first report of this congenital anomaly associated with this syndrome.

Adult↗
PubMed1979

Pagetoid reticulosis (Woringer-Kolopp disease).

Two patients with solitary lesions of pagetoid reticulosis are presented. A third case with disseminated lesions and similar microscopic detail is also reported. Lighg microscopic findings include an abnornal cell infiltrate confined to the epidermis and distributed diffusely in a pagetoid pattern. In ultrathin sections, the abnormal cells are seen to have an abundant cytoplasm with numerous organelles and a convoluted nucleus, often with a prominent nucleolus. The nature of the abnormal cells is discussed. The infiltrate is differentiated from that of mycosis fungoides.

Adult↗
PubMed1979

Skin levels and vasoconstrictor assay of topically applied hydrocortisone.

Ointment containing 2.5% hydrocortisone was applied topically under occlusion to 84 subjects. Fifty-three percent of the population showed skin blanching in response to topical application of the steroid. To correlate vasoconstrictor response with drug level, hydrocortisone concentrations were determined fluorometrically in skin samples from 16 subjects in whom skin blanching was also assessed. The epidermal concentration of hydrocortisone was significantly greater in those subjects who exhibited blanching. Data suggest that a minimum epidermal reservoir of 200 micrograms of hydrocortisone per gram of lyophilized tissue is necessary to elicit a definite vasoconstrictor response.

Administration, Topical↗
PubMed1978

Growth rate of cultured human fibroblasts increased by glucocorticoids.

Selected glucocorticoids have been demonstrated to increase the growth rate of human skin fibroblasts in culture, over a physiologically significant concentration range. At the same concentrations and identical conditions, the glucocorticoid compounds tested inhibited the growth rate of mouse L-929 cells. We have discussed currently acceptable theories of glucocorticoid mechanism of action that permit this dichotomous effect, the main point being that inhibition can no longer be regarded as the only response of fibroblasts to glucocorticoids. Conclusions drawn from observations of cell cultures affected by addition of glucocorticoids must have considered the source of the cells, as response may vary with source and biologic state of the cells in culture.

Adult↗
PubMed1977

Comparative immunochemistry of bacterial, algal and plant ferredoxins.

1. Antibodies were produced in rabbits to the 4Fe-4S ferrodoxins from Bacillus stearothermophilus, the 2 [4Fe-4S] ferredoxin from Clostridium pasteurianum, and the 2Fe-2S ferredoxins from the blue-green algia Spirulina maxima, the green alga Scenedesmus obliquus, and the higher plant Beta vulgaris. The antibodies were tested for immunoprecipitation activity with seven bacterial, twelve blue-green algal, six eukaryotic algal and six higher plant ferredoxins. 2. Antibodies to the bacterial ferredoxins reacted to a significant extent only with their homologous proteins. On the other hand, antibodies to the plant and algal ferredoxins showed cross-reaction with other ferredoxins. There was a correlation between the degrees of immunoprecipitation and the similarity in amino acid sequences. These results suggest that the method can be used as a marker in taxonomic studies. 3. The interaction of the antibodies with the five native ferredoxins was compared with the reactions with their apoproteins. In each case the degree of interaction was different. This behaviour was interpreted as due to an influence of tertiary structure on the antibody-antigen interaction.

Amino Acid Sequence↗
PubMed1976

Photosynthetic electron transport, ATP synthesis and nitrogenase activity in isolated heterocysts of Anabaena cylindrica.

Isolated heterocysts of the N2-fixing blue-green alga Anabaena cylindrica contain the Photosystem I components P-700, bound and soluble ferredoxins and ferredoxin-NADP reductase. They also show Photosystem I activity being able to photoreduce both methylviologen and NADP when ascorbate + dichlorophenol-indophenol acts as reductant. They photophosphorylate (64 munol ATP produced/mg chlorophyll a/h) and carry out oxidative phosphorylation (8.7 munol ATP produced/mg chlorophyll a/h). Ninety per cent of the total cell-free extract nitrogenase activity is located in the heterocyst fraction of aerobic cultures.

Adenosine Triphosphate↗
PubMed1976

The incorporation of nitrogen into products of recent photosynthesis in Anabaena cylindrica Lemm.

In vivo tracer studies with 14C have been performed to help determine pathways of incorporation of newly assimilated nitrogen into N2-fixing cells of Anabaena cylindrica. After photosynthesis in Ar: O2:14CO2 for 30 min, the addition of N2 or NH+4 resulted in increased rates of 14CO2-incorporation both in the light and dark, and in increased incorporation of 14C into amino acids at the expense of sucrose and sugar phosphates. Evidence of enhanced sucrose catabolism and increased pyruvate kinase activity was obtained on adding nitrogen, and, of the 14C-labelling entering the tricarboxylic acid cycle, more appeared in citrate and 2-oxoglutarate than in malate and oxaloacetate. The kinetics of 14C-incorporation into various amino acids suggest that in the light and dark the most important route of primary ammonia assimilation involves glutamine synthetase and that glutamate, aspartate, glycine and probably alanine are formed secondarily from glutamine.

Alanine↗
PubMed1976

ATP pools and transientss in the blue-green alga, Anabaena cylindrica.

Anabaena cylindrica grown in steady state continuous culture has an extractable ATP pool, measured on the basis of the luciferin-luciferase assay of 165 +/- 35 nmoles ATP mg chla-1. This pool is maintained by a dynamic balance between the rate of ATP synthesis and the rate of ATP utilization. Phosphorylating mechanisms which can maitain the pool in the short term are total photophosphorylation, cyclic photophosphorylation and oxidative phosphorylation. The alga can maintain its ATP pool by switching rapidly from one of these phosphorylating mechanisms to another depending on the environmental conditions. At each switch-over there is a transient drop in the ATP pool for a few seconds. On switching to conditions where only substrate level phosphorylation operates, the ATP pool falls immediately, but takes several hours to recover. The apparent rates of ATP synthesis by total photophosphorylation and by cyclic photophosphorylation are both much higher (210 +/- 30 and 250 +/- 13 mumoles ATP mg chla-1 h-1 respectively) than the apparent rate of ATP synthesis by oxidative phosphorylation (22 +/- 3 mumoles ATP mg chla-1 h-1). In long term experiments the ATP pool is maintained when total photophosphorylation is operating. It cannot be maintained in the long term by cyclic photophosphorylation alone in the absence of photosystem II activity in endogenous carbon compounds, or by oxidative phosphorylation in the absence of endogenous carbon compounds. Measurements of ATP, ADP and AMP show that the total pool of adenylates is similar in the light and in the dark in the short term. There is only limited production of ATP under dark anaerobic conditions when glycolysis and substrate phosphorylation can operate which suggests that these processes are of limited significance in providing ATP in Anabaena cylindrica.

Adenosine Triphosphate↗