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Biomedical subjects

D C White

Publications and source records attributed to D C White.

At least 181 records · Page 10Linked to original sources
PubMed1978

High density tissue culture on microporous membranes perfused by blood: report of a new bioartificial system.

A new tissue culture system has been developed to support high density cell growth using the sheep as the host. Cellular nutrition is provided by plasma solutes as they diffuse from arterial blood across microporous polycarbonate membranes into a device attached to an arteriovenous shunt. Culture chambers are constructed with transparent polycarbonate to allow photomicroscopy of the tissue in situ. System performance is demonstrated by the high density growth of fetal sheep thymus allografts and rat soft tissue sarcoma xenografts.

Animals↗
PubMed1977

Muramic acid as a measure of microbial biomass in estuarine and marine samples.

Muramic acid, a component of the muramyl peptide found only in the cell walls of bacteria and blue-green algae, furnishes a measure of detrital or sedimentary procaryotic biomass. A reproducible assay involving acid hydrolysis, preparative thin-layer chromatographic purification, and colorimetric analysis of lactate released from muramic acid by alkaline hydrolysis is described. Comparison of semitropical estuarine detritus, estuarine muds, and sediments from anaerobic Black Sea cores showed muramic acid levels of 100 to 700 microng/g (dry weight), 34 microng/g, and 1.5 to 14.9 microng/g, respectively. Enzymatic assays of lactate from muramic acid gave results 10- to 20-fold higher. Radioactive pulse-labeling studies showed that [14C]acetate is rapidly incorporated into muramic acid by the detrital microflora. Subsequent loss of 14C, accompanied by nearly constant levels of total muramic acid, indicated active metabolism in procaryotic cell walls.

Acetates↗
PubMed1977

Use of lipid composition and metabolism to examine structure and activity of estuarine detrital microflora.

Earlier studies have shown that the activity of the estuarine detrital microflora measured by various enzyme activities, muramic acid and adenosine 5'-triphosphate (ATP) content, heterotrophic potentials, and respiratory activities correlates with the incorporation of C and P into the microbial lipids. In this study, these lipids were reproducibly fractionated into neutral lipid, glycolipid, and phospholipid classes. Distinct differences between the active microflora of oak leaves, sweet gum leaves, and pine needles were evidenced both in the rate of lipid synthesis and in the proportions of neutral lipids, glycolipids, and phospholipids. Successional changes in the microflora of leaves incubated in a semitropical estuary, previously suggested by ATP-to-muramic acid ratios and scanning electron micrography, were reflected in changes in the proportions of C in major lipid classes when analyzed from the same type of detritus. Short incubation times with C gave lipid compositions rich in phospholipids that are typical for the faster-growing bacterial populations; longer incubation with C gave lipid compositions richer in neutral and glycolipids, more characteristic of slower-growing eukaryotes or morphologically more complex prokaryotes. The metabolism of the lipids of the estuarine detrital microflora was examined by a pulse-chase experiment with C. Glycolipids lost C at a rate equal to the loss of C of the slow component of muramic acid. Individual phospholipids lost C from their backbone glycerol esters at different rates.

Journal Article↗
PubMed1977

Severe radiation injuries of the lung.

The lung is a radiosensitive organ whose limited tolerance must be treated with great respect in the radiation management of malignant tumors in the thorax. Severe radiation pneumonopathy can cripple and kill as the outcome of faulty judgment, error, accident, or calculated risk in an effort to control a locally advanced cancer. The clinical and radiologic profile of this unique and challenging syndrome is described and the histopathology and pathogenesis are reviewed. The clinical and technical factors of high risk are discussed, and guidelines for therapeutic management and safer clinical practice are offered.

Adrenal Cortex Hormones↗
PubMed1976

Oxidation and reduction of membrane-bound cytochrome c in Hemophilus parainfluenzae. Reaction with oxygen, hydrogen peroxide and nitrate.

Cytochromes of the a-, b-, c- and d-type become reduced when intact cells of Hemophilus parainfluenzae have become anaerobic following respiration with substrates such as formate or succinate, as shown previously (J. Biol. Chem. (1970) 254, 5096-5100). In the presence of formate after depletion of O2, there is an unusual two-step time course of reduction of the membrane-bound cytochrome c. The proportion of the cytochrome c which is reduced during the second stage is oxidizable by either nitrate or H2O2 and is reduced again when the nitrate or H2O2 have been depleted. We conclude that the observed two-stage reduction of cytochrome c results from the presence of an oxidant, probably H2O2, produced by reaction of formate dehydrogenase with O2. This was shown by the effects of cyanide, catalase and O2. In addition, no evidence for the production of the oxidant is seen when succinate is the substrate oxidized. Although measurements of absorption spectra indicated only one species of cytochrome c, kinetic evidence is presented for some separation of the cytochrome c into more than one electron transport pathway.

Binding Sites↗
PubMed1976

The histopathologic basis for functional decrements in late radiation injury in diverse organs.

As more and more patients respond favorably to combined cancer therapies, the time of survival from radiotherapy will become the most important single factor in the incidence and progression of late radiation changes. The late sequelae of irradiation are the sum of the following: 1) residua of the direct and indirect early changes in responsive cell populations; 2) progressive vascular sclerosis with its associated effect upon connective tissue and the parenchymal cells; and 3) the reactive or replacement connective tissue proliferation which is responding to 1) and 2). From this it may be seen that further investigative efforts need direction toward: 1) reducing the magnitude and permanence of the early principal parenchymal cell injury; 2) diminishing the severity of the early microvascular change which adds significantly to the early parenchymal cell damage; 3) determining the mechanics of the progressive vascular sclerosis with a view to retarding this effect; and 4) lessening the reactive fibrosis.

Blood Vessels↗
PubMed1975

Mechanical and biochemical cycles in muscle contraction.

The current biochemical approach to understanding the mechanism by which chemical energy is converted into mechanical energy in muscle is by investigating the kinetics of the reaction of ATP with the isolated contractile proteins in solution with stopped and quenched flow techniques. The results are interpreted in terms of a cycle of hydrolysis of ATP. The current mechanical approach lies through the kinetics of force production or length change in preparations with the contractile proteins intact, by following step changes in length or tension. The results are usually interpreted in terms of mechanical cycles of activity of cross-bridges, in which a cross-bridge progresses through a series of states with different mechanical properties. If the biochemist's and the mechanist's cycles are one and the same, a problem arises over the correspondence between states in the two cycles. One approach to answering this question is through the determination of the effect of pH and of such substances as ATP, ADP and inorganic orthophosphate on the mechanical response. We hope that these will act at known points in the biochemist's cycle and their influence upon the mechanical cycle should enable their location here to be ascertained. The paper deals with the effects of phosphate, ATP and magnesium ions on the mechanical response of insect flight muscle.

Actins↗
PubMed1975

Role of vitamin K2 in the organization and function of Staphylococcus aureua membranes.

A mutant of Staphylococcus aureus auxotrophic for menadione (a vitamin K2 precursor) was used to study the effects of menadione deprivation on the structure and function of the cell membrane. The phospholipid composition and metabolism was essentially unaltered by menadione deprivation. Removal of this percursor caused cellular levels of the cytochromes, protoheme, vitamin K2, and several membrane-bound flavoprotein dehydrogenase activities to decrease as a function of growth dilution. The cytochromes were enzymatically reducible and maintained in the same proportions as menadione-supplemented cells. Oxidative phosphorylation, however, was reduced more than 10-fold and membrane vesicles obtained from menadione-deprived cells were unable to couple glycine transport to L-lactate oxidation. Succinic dehydrogenase and adenosine 5' triphosphate hydrolysis appeared unaffected by menadione deprivation. These data suggest that menadione deprivation in the mutant stops the synthesis of vitamin K2 and other electron transport chain components and prosthetic groups. Although individual electron transport chain members remained fully functional during menadione deprivation, the overall efficiency of the chain, measured in terms of its function in electron transport, oxidative phosphorylation, and electron transport chain-linked transport, dropped greatly. This suggests that the synthesis of vitamin K2 is modulated to the synthesis of other components of the electron transport system, and that their organization into a functional system requires a specific concentration of vitamin K2 with respect to total membrane lipid.

Adenosine Triphosphate↗