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Biomedical subjects

D R Evans

Publications and source records attributed to D R Evans.

140 records · Page 8Linked to original sources
PubMed1972

ATC displays.

The impact of system implementation on the display problem is examined, and future possibilities to ease present problems are discussed. It is stressed that display solutions should always be examined in relation to user requirement. This paper was first given as a keynote address at the IEE Displays Conference at Loughborough University of Technology, 7-10 September 1971.

Journal Article↗
PubMed1972

The thiol group in the catalytic chains of aspartate transcarbamoylase.

The allosteric enzyme aspartate transcarbamoylase (EC 2.1.3.2) was previously shown to consist of two functionally distinct types of polypeptide chains. X-ray diffraction and chemical studies showed that there are six copies of both catalytic (C) and regulatory (R) chains, and that the intact molecular complex (C(6)R(6)) has D(3) symmetry. Organomercurials react preferentially with the four thiol groups on each R chain, dissociating the molecular complex. We show that 2-chloromercuri-4-nitrophenol reacts specifically and rapidly with the single C-chain thiol, which is believed to be near the catalytic site. This reaction inactivates the enzyme in solution and does not dissociate the molecular complex. Spectrophotometric titration and mercury analysis indicates that six molecules of this mercurial are firmly bound to the enzyme (R(6)C(6)), and crystallographic studies establish that only six sites, related by D(3) symmetry, are modified. The known low reactivity of this C-chain thiol with other sulfhydryl reagents, the unusual structural requirements in the reaction with 2-chloromercuri-4-nitrophenol, and the spectral properties of the resulting derivative provide insight into the environment of this thiol. Probably, at least one positively charged group of the enzyme is nearby, and the environment of this thiol is at least partially hydrophobic.

Allosteric Regulation↗
PubMedDate not supplied

A factor VIII concentrate of intermediate purity and higher potency.

A fractionation method has been modified to produce a factor VIII concentrate of intermediate purity and a potency of about 12 iu/ml, suitable for injection by syringe. The solubility, ease of filtration and purity of the concentrate have been improved by including a stage in which contaminants are precipitated at controlled temperature, pH and ionic strength. A summary of the first 50 production-scale batches is presented. Plasma can be harvested from whole blood and frozen within eight hours of donation, or after overnight storage of whole blood, with no significant difference in overall yield.

Factor VIII↗
PubMedDate not supplied

Third-trimester amniotic fluid metal levels associated with preeclampsia.

Studies of maternal amniotic fluid and serum at delivery have revealed the presence of toxic metals or deficiencies of essential metals associated with high-risk pregnancy. Essential and toxic metal levels were studied in 29 preeclamptic and 101 normal pregnancies. The authors grouped the samples according to the following gestation ages: 33-36 wk (48 normal and 10 preeclamptic) and 37-40 wk (53 normal and 19 preeclamptic). The metals studied were calcium, magnesium, zinc, selenium, copper, cadmium, and lead. Comparisons of the 33-36-wk gestation group showed significant differences between normal and preeclamptic amniotic fluid in levels of lead, calcium, magnesium, zinc, and selenium. There were also significant differences in levels of magnesium, copper, zinc, cadmium, and lead during the gestation period of 37-40 wk. The changes observed in calcium and lead levels were consistent with the results of animal studies in which investigators have found depressed calcium transport associated with subacute or chronic lead poisoning, resulting in a physical syndrome similar to preeclampsia.

Amniotic Fluid↗