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Biomedical subjects

A C Durham

Publications and source records attributed to A C Durham.

At least 19 recordsLinked to original sources
PubMed1983

A survey of readily available chelators for buffering calcium ion concentrations in physiological solutions.

Stability constants are reported for the binding of H+, Ca2+ and Mg2+ ions to the chelators commonly abbreviated EGTA, EDTA, HEDTA, DPA, NTA, ADA, and citrate, under uniform conditions of physiological temperature and ionic strength. Other compounds usable as calcium buffers are listed. The theoretical and practical considerations that influence the actual pCa attained in a chelator solution are discussed and a Hepes-buffered saline solution is suggested as a standard of "physiological pH". With these figures it is possible to make a rational choice of chelator to control the pCa and pMg of solutions for investigations in cell physiology, drug action, virus reproduction, and ion binding to proteins.

Buffers↗
PubMed1983

A survey of the available colorimetric indicators for Ca2+ and Mg2+ ions in biological experiments.

The binding of Ca2+ and Mg2+ ions to commercially available and easily synthesizable metallochromic indicators has been systematically examined at pH 7.35, temperature 37 degrees C, ionic strength 0.16, the conditions of blood plasma. The pCa and pMg midpoints of the colour changes of all the useful indicators are reported. In addition to the well-known indicators arsenzazo III, chlorophosphonazo III, antipyrylazo III, and murexide for Ca2+, and Eriochrome Black T and Eriochrome Blue SE for Mg2+, we draw attention to the values of oxyacetazo I, carboxyazo III, tropolone, methylthymol blue, Mordant Black 32, and the tetracyclines.

Azo Compounds↗
PubMed1982

Calcium ions and the control of proliferation in normal and cancer cells.

Several lines of evidence suggest tha Ca2+ ions control cell proliferation: Ca2+ entry into cytoplasm acts as a general mitogen; serum and serum-replacements induce Ca2+ influx; the Ca2+ concentrations in growth media required to support the proliferation of normal cells are much higher than those required for cancer cells; serum and growth factors reduce the Ca2+ requirements of normal cells; tumour promoters alter Ca2+ fluxes via a mechanism used principally by growth factors. Minor supporting evidence includes the effects of various drugs and viruses, and the behaviour of tumour cell mitochondria and intercellular junctions. It is still not possible to decide exactly where and when inside cells the critical effect of Ca2+ on proliferation occurs, but we discuss at length the practical problems of understanding Ca2+ movements in tissue-culture cells. Carried to its logical conclusion, present evidence suggests that an overridden or bypassed Ca2+ control process may be the key, common determinant of unrestrained proliferation in cancer cells.

Animals↗
PubMed1981

The generality of cation-binding sites in rod-shaped viruses.

Hydrogen-ion titration curves have been measured for two filamentous plant viruses (clover yellow mosaic virus and potato virus X) and two filamentous bacterial viruses (fd and Pf1) with and without Ca2+ or Mg2+ ions present, and for the protein of the PM6 mutant of tobacco mosaic virus. The bacterial viruses do not possess the 'strong' cation-binding sites found in all plant viruses, but they have 'weak' sites that can be assigned to juxtaposed carboxylate groups on their external surfaces. The strong sites in plant viruses still cannot be assigned to any particular amino-acid side chains, but they must be located in the region of high electronegativity near the axis.

Bacteriophages↗
PubMed1978

The roles of small ions, especially calcium, in virus disassembly, takeover, and transformation.

Three related hypotheses are proposed. (1) Many simple viruses disassemble in the act of crossing a membrane, drawing energy from ionic disequilibria across the membrane. (2) Many of the metabolic changes early in virus infection are due to altered ion fluxes across membranes and the consequently altered ion concentrations in cytoplasm. (3) The crucial determinant of the transformed phenotype is also a change in ion concentrations. Ca2+ ions may play a major role in these effects.

Calcium↗
PubMed1977

Hydrogen-ion binding by tobacco-mosaic-virus protein polymers.

Hydrogen ion titration curves of tobacco mosaic virus protein have been measured in various conditions of protein concentration, temperature, ionic strength, and rate of pH change. The polymers present at each stage are deduced from turbidity and sedimentation data, plus published information. A simple semi-quantitative analysis of the curves is given, and the pK values of the two abnormal carboxylates in single helix are estimated as 6.4 and about 7.0. Disks, and some faster-forming unknown polymers in the same size range, have been abnormal carboxylate with pK 6.9. These results are most easily interpreted in terms of electrostatic interactions between carboxylates, probably at the axial ends of the protein subunits.

Hydrogen-Ion Concentration↗
PubMed1976

Control of chemotaxis in Physarum polycephalum.

Plasmodia migrate towards those situations which increase the frequency of their alternations in streaming, and away from those which decrease the frequency. Therefore peristalsis-like waves in Physarum move in the direction opposite from the net movement of the organism. The mechanism is fundamentally related to other known types of chemotaxis.

Chemotaxis↗
PubMed1976

Oscillations of calcium ion concentrations in Physarum polycephalum.

Aequorin is a photoprotein which emits light in response to changes in free calcium concentration. When aequorin was microinjected into plasmodia of Physarum polycephalum, light emission varied in synchrony with the motile oscillations of the organisms. Therefore, movement is correlated which changes in the concentration of free calcium.

Aequorin↗
PubMed1975

A prediction of the structure of tobacco-mosaic-virus protein.

The location of amino acid residues within the tobacco mosaic virus protein subunit is discussed. Sequence data, X-ray crystallographic measurements, and the availability of specific residues for enzymic, immunological or chemical reaction are amongst the information used to trace roughly how the tobacco mosaic virus polypeptide chain winds in and out from the virus axis. Published rules for predicting secondary structure are then applied to obtain a diagram of the course of the polypeptide chain. This map should be useful for the interpretation of X-ray diffraction data and already permits an outline of the main features of the inner third of subunit to be suggested.

Amino Acid Sequence↗