Electron tunneling in biological molecules

Electron transfers in photosynthesis and respiration commonly occur between protein-bound prosthetic groups that are separated by large molecular distances (often greater than 10Å). Although the electron donors and acceptors are expected to be weakly coupled, the reactions are remarkably fast and proceed with high specificity. Tunneling timetables based on analyses of Fe^(2+)/Cu^+ to Ru^(3+) electron-transfer rates for Ru-modified heme and copper proteins reveal that the structure of the intervening polypeptide can control these distant donor-acceptor couplings. Multistep tunneling can account for the relatively rapid Cu^+ to Re^(2+) electron transfer observed in Re-modified azurin

Electron tunneling in rhenium-modified Pseudomonas aeruginosa azurins

Laser flash-quench methods have been used to generate tyrosine and tryptophan radicals in structurally characterized rhenium-modified Pseudomonas aeruginosa azurins. Cu(I) to “Re(II)” electron tunneling in Re(H107) azurin occurs in the microsecond range. This reaction is much faster than that studied previously for Cu(I) to Ru(III) tunneling in Ru(H107) azurin, suggesting that a multistep (“hopping”) mechanism might be involved. Although a Y108 radical can be generated by flash-quenching a Re(H107)M(II) (M=Cu, Zn) protein, the evidence suggests that it is not an active intermediate in the enhanced Cu(I) oxidation. Rather, the likely explanation is rapid conversion of Re(II)(H107) to deprotonated Re(I)(H107 radical), followed by electron tunneling from Cu(I) to the hole in the imidazole ligand

Call-duration and triage decisions in out of hours cooperatives with and without the use of an expert system

<p>Abstract</p> <p>Background</p> <p>Cooperatives delivering out of hours care in the Netherlands are hesitant about the use of expert systems during triage. Apart from the extra costs, cooperatives are not sure that quality of triage is sufficiently enhanced by these systems and believe that call duration will be prolonged drastically. No figures about the influence of the use of an expert system during triage on call duration and triage decisions in out of hours care in the Netherlands are available.</p> <p>Methods</p> <p>Electronically registered data concerning call duration and triage decisions were collected in two cooperatives. One in Tilburg, a cooperative in a Southern city of the Netherlands using an expert system, and one in Groningen, a cooperative in a Northern city not using an expert system. Some other relevant information about the care process was collected additionally. Data about call duration was compared using an independent sample t-test. Data about call decisions was compared using Chi Square.</p> <p>Results</p> <p>The mean call time in the cooperative using the TAS expert system is 4.6 minutes, in the cooperative not using the expert system 3.9 minutes. A significant difference of 0.7 minutes (0.4 – 1.0, 95% CI) minutes. In the cooperative with an expert system a larger percentage of patients is handled by the assistant, patients are less often referred to a telephone consultation with the GP and are less likely to be offered a visit by the GP.</p> <p>A quick interpretation of the impact of the difference in triage decisions, show that these may be large enough to support the hypothesis that longer call duration is compensated for by less contacts with the GP (by telephone or face-to-face). There is no proof, however, that these differences are caused by the use of the triage system. The larger amount of calls handled by the assistant may be partly caused by the fact that the assistants in the cooperative with an expert system more often consult the GP during triage. And it is not likely that the larger amount of home visits in Groningen can be attributed to the absence of an expert system. The expert system only offers advice whether a GP should be seen, not in which way (by consultation in the office or by home visit).</p> <p>Conclusion</p> <p>The differences in call times between a cooperative using an expert system and a cooperative not using an expert system are small; 0.4 – 1.0 min. Differences in triage decisions were found, but it is not proven that these can be contributed to the use of an expert system.</p

Knowledge and Awareness of Congenital Cytomegalovirus Among Women

Background. Congenital cytomegalovirus (CMV) infection is a leading cause of disabilities in children, yet the general public appears to have little awareness of CMV. Methods. Women were surveyed about newborn infections at 7 different geographic locations. Results. Of the 643 women surveyed, 142 (22%) had heard of congenital CMV. Awareness increased with increasing levels of education (P < .0001). Women who had worked as a healthcare professional had a higher prevalence of awareness of CMV than had other women (56% versus 16%, P < .0001). Women who were aware of CMV were most likely to have heard about it from a healthcare provider (54%), but most could not correctly identify modes of CMV transmission or prevention. Among common causes of birth defects and childhood illnesses, women's awareness of CMV ranked last. Conclusion. Despite its large public health burden, few women had heard of congenital CMV, and even fewer were aware of prevention strategies

Outer-Sphere Contributions to the Electronic Structure of Type Zero Copper Proteins

Bioinorganic canon states that active-site thiolate coordination promotes rapid electron transfer (ET) to and from type 1 copper proteins. In recent work, we have found that copper ET sites in proteins also can be constructed without thiolate ligation (called “type zero” sites). Here we report multifrequency electron paramagnetic resonance (EPR), magnetic circular dichroism (MCD), and nuclear magnetic resonance (NMR) spectroscopic data together with density functional theory (DFT) and spectroscopy-oriented configuration interaction (SORCI) calculations for type zero Pseudomonas aeruginosa azurin variants. Wild-type (type 1) and type zero copper centers experience virtually identical ligand fields. Moreover, O-donor covalency is enhanced in type zero centers relative that in the C112D (type 2) protein. At the same time, N-donor covalency is reduced in a similar fashion to type 1 centers. QM/MM and SORCI calculations show that the electronic structures of type zero and type 2 are intimately linked to the orientation and coordination mode of the carboxylate ligand, which in turn is influenced by outer-sphere hydrogen bonding

The Cu_A Center of a Soluble Domain from Thermus Cytochrome ba_3. An NMR Investigation of the Paramagnetic Protein

The Cu_A center in subunit II of cytochrome c oxidase, the terminal enzyme of aerobic respiration, transfers electrons from cytochrome c to the proton-pumping machinery in subunit I. The unique electronic absorption and EPR spectra of Cu_A exclude it from classification with the well-studied biological copper centers. High-resolution X-ray structures of Cu_A-containing proteins reveal two copper atoms approximately 2.5 Å apart, bridged by two cysteine sulfurs. Each Cu has a terminal histidine ligand and a weak ligand, methionine for one and a main chain carbonyl for the other. These structures are consistent with earlier EPR measurements and theoretical calculations, which predicted a highly delocalized mixed-valence [Cu(II),Cu(I)] Cu_A site. Here we report ^1H NMR measurements at 600 MHz on a soluble Cu_A domain from Thermus thermophilus cytochrome ba_3

Properties of Photogenerated Tryptophan and Tyrosyl Radicals in Structurally Characterized Proteins Containing Rhenium(I) Tricarbonyl Diimines

Aromatic amino acid radicals are key intermediates in nucleic acid biosynthesis, DNA repair, dioxygen reduction by cytochrome oxidase, water oxidation by PSII, as well as other biological procesess. In our work on electron tunneling in proteins, we have developed laser flash/quench methods that potentially could facilitate the study of such highly reactive radicals. To test our methods, we are investigating two structurally characterized proteins, [Re(CO)_3(L)(H83)]^+AzM^(2+) and [Re(CO)_3(L)(H107)]^+AzM^(2+) (L ) 1,10-phenanthroline (phen) or 4,7-Me_2phen; Az ) Pseudomonas aeruginosa azurin; M ) Cu or Zn). Of special interest is that calculations and experiments on the H107 protein show that Cu^+ oxidation via electron transfer (ET) through an intervening tyrosine (Cu^+ → Y108^(./) → Re(2+)) is over 2 orders of magnitude faster than optimized (Cu^+ → Re^(2+)) electron tunneling