Engineering tyrosine-based electron flow pathways in proteins: The case of aplysia myoglobin

Tyrosine residues can act as redox cofactors that provide an electron transfer ("hole-hopping") route that enhances the rate of ferryl heme iron reduction by externally added reductants, for example, ascorbate. Aplysia fasciata myoglobin, having no naturally occurring tyrosines but 15 phenylalanines that can be selectively mutated to tyrosine residues, provides an ideal protein with which to study such through-protein electron transfer pathways and ways to manipulate them. Two surface exposed phenylalanines that are close to the heme have been mutated to tyrosines (F42Y, F98Y). In both of these, the rate of ferryl heme reduction increased by up to 3 orders of magnitude. This result cannot be explained in terms of distance or redox potential change between donor and acceptor but indicates that tyrosines, by virtue of their ability to form radicals, act as redox cofactors in a new pathway. The mechanism is discussed in terms of the Marcus theory and the specific protonation/deprotonation states of the oxoferryl iron and tyrosine. Tyrosine radicals have been observed and quantified by EPR spectroscopy in both mutants, consistent with the proposed mechanism. The location of each radical is unambiguous and allows us to validate theoretical methods that assign radical location on the basis of EPR hyperfine structure. Mutation to tyrosine decreases the lipid peroxidase activity of this myoglobin in the presence of low concentrations of reductant, and the possibility of decreasing the intrinsic toxicity of hemoglobin by introduction of these pathways is discussed. © 2012 American Chemical Society

Nitrogen loading of shallow groundwater aquifers in varying soil and topographic settings of southwestern Indiana

Presented at the Geological Society of America Meeting (22–25 October 2006), Philadelphia, PennsylvaniaNumerous sources of nitrogen capable of impacting groundwater exist in rural areas of the midwestern United States. These sources include commercial and non-commercial fertilizers as well as on-site septic distribution systems. Over the past three years, we have undertaken detailed monitoring studies aimed at quantifying nitrate loading of shallow groundwater aquifers resulting from natural recharge at seven sites in southwestern Indiana. The sites occur in a variety of topographic settings and are associated with both well drained and poorly drained soils. Measured changes in soil-moisture profiles were used along with continuous measurements of precipitation and potential evapotranspiration to calculate the storage and movement of groundwater in the unsaturated zone. Nitrate loading of the shallow aquifers was then calculated by combining the flow rate with analytical data on solute chemistry from multiple depths within the unsaturated zone. The results of these calculations show that the highest loading rates occur at the study sites adjacent to agricultural fields treated with commercial and non-commercial (manure) fertilizers. The calculated nitrogen loading at these three sites ranged from 21 to as high as 136 kg of N per hectare (the highest loading rate occurred at the site where the manure was applied). In contrast, much lower loading rates were calculated using data collected from four sites associated with residential on-site septic distribution systems. In these cases, the calculated nitrogen loading values were an order of magnitude lower and ranged from 1.3 to 7.4 kg of N per hectare. These findings have implications for land-use management and have been used to guide the compilation of GIS-based maps that identify high- and low-risk areas throughout Indiana. This was accomplished by evaluating areas on the basis of soil characteristics and unsaturated zone thicknesses.Funding provided by a U.S. EPA Clean Water Act Section 104(b)(3) Water Quality Cooperative Agreements/Grants Program and a Cooperative Agreement between IGS and the Indiana State Department of Healt

On the elliptic nonabelian Fourier transform for unipotent representations of p-adic groups

In this paper, we consider the relation between two nonabelian Fourier transforms. The first one is defined in terms of the Langlands-Kazhdan-Lusztig parameters for unipotent elliptic representations of a split p-adic group and the second is defined in terms of the pseudocoefficients of these representations and Lusztig's nonabelian Fourier transform for characters of finite groups of Lie type. We exemplify this relation in the case of the p-adic group of type G_2.Comment: 17 pages; v2: several minor corrections, references added; v3: corrections in the table with unipotent discrete series of G

Alternatively spliced variants of the cell adhesion molecule CD44 and tumour progression in colorectal cancer.

Increased expression of alternatively spliced variants of the CD44 family of cell adhesion molecules has been associated with tumour metastasis. In the present study, expression of alternatively spliced variants of CD44 and their cellular distribution have been investigated in human colonic tumours and in the corresponding normal mucosa, in addition to benign adenomatous polyps. The expression of CD44 alternatively spliced variants has been correlated with tumour progression according to Dukes' histological stage. CD44 variant expression was determined by immunohistochemisty using monoclonal antibodies directed against specific CD44 variant domains together with RT-PCR analysis of CD44 variant mRNA expression in the same tissue specimens. We demonstrate that as well as being expressed in colonic tumour cells, the full range of CD44 variants, CD44v2-v10, are widely expressed in normal colonic crypt epithelium, predominantly in the crypt base. CD44v6, the epitope which is most commonly associated with tumour progression and metastasis, was not only expressed by many benign colonic tumours, but was expressed as frequently in normal basal crypt epithelium as in malignant colonic tumour cells, and surprisingly, was even absent from some metastatic colorectal tumours. Expression of none of the CD44 variant epitopes was found to be positively correlated with tumour progression or with colorectal tumour metastasis to the liver, results which are inconsistent with a role for CD44 variants as indicators of colonic cancer progression

Taphonomic Comparisons of Two Laurentian Upper Ordovician Epeiric Sea “Small Shelly Faunas”

The Elgin Member of the Upper Ordovician (Katian) Maquoketa Formation of Iowa contains phosphorite beds consisting of millimeter-scale phosphatic fossils, primarily steinkerns. Similar beds occur in the coeval strata of the classic Cincinnatian Series around the Cincinnati, Ohio area. Initial sampling of the phosphate-rich beds of the Maquoketa allows comparison between the faunal composition and taphonomy of these beds and collections from the more extensively sampled Cincinnatian strata. We isolated these fossils by dissolution of bulk samples in acetic acid and examined the same strata in thin section to study the fossils in context. The Maquoketa diminutive phosphatized fossils have been interpreted as evidence of dwarfed faunas indicative of environmental stress, such as anoxia, which may have also contributed to phosphogenesis. An alternative explanation for the small size is that phosphogenesis was size-selective and that phosphatic particles were concentrated by reworking as less-durable shell material was destroyed. These hypotheses can be tested by examining the fauna for “normal” sized elements. Insoluble residue from sampled phosphate-rich strata in both field areas yields abundant molluscan steinkerns, as well as crinoid columnals, conodonts, scolecodonts, bryozoan zooecia steinkerns and other fossils associated with a normal marine fauna. In Cincinnatian occurrences, the composition of the phosphatic assemblages is variable but is a reflection of the variability of faunal composition seen in these strata rather than an indication of an unusual fauna associated with extreme conditions; most are associated with diverse marine assemblages. Insoluble residues from both areas yield steinkerns that precipitated in small pores within larger skeletons. This phenomenon can be seen in thin section, where phosphate is present within certain parts of the larger preserved skeletons. The maximum size of the steinkerns of the Maquoketa is larger than those of most Cincinnatian occurrences, although size is variable in Cincinnatian occurrences. In Cincinnatian strata the abundance of small phosphatic fossils correlates with evidence for reworking; heavily reworked beds yield the most residue. Examined in thin section, the sampled strata of the Maquoketa appear to be heavily reworked and represent an extreme endmember of this concentration of durable phosphatic material. Detailed examination using an SEM and associated XRF elemental mapping reveals that the phosphatic steinkerns of both localities are very similar in their taphonomy. Both consist of botryoidal growths of carbonate fluorapatite (CFA). The botryoidal growth appears to have nucleated on the walls of the original shell, first forming a lining of variable thickness. Some steinkerns have secondary botryoidal growths on the outside of the steinkern indicating continued precipitation of CFA after destruction of the original shell. This secondary precipitation suggests that reworking played a role not only in concentrating the phosphatic material but also in encouraging continued precipitation of CFA. The size of the available pore space appears to have played a role in encouraging the precipitation of CFA. In thin section the CFA is limited to smaller parts of larger shells, such as the apices of gastropods and did not precipitate on the inside of the larger, more open spaces within the shell. Many of the phosphate-filled spaces are also sediment-filled, suggesting that subdivision of the larger space into smaller pores enhanced the precipitation of CFA. The difference in the maximum size of the steinkern achieved in the different assemblages suggests that geochemical factors affected size limits. The most distinctive aspect of phosphate-rich Ordovician strata of mid-Laurentia is the degree of reworking that concentrated the durable small fossils. Details of taphonomy also suggest that phosphate precipitation was an iterative process enhanced by reworking, and that small pore spaces enhanced this mineralization, thus selectively preserving certain sizes and parts of the larger fauna

Cochlear Implants in the Workplace: A Nationwide Survey

A nation wide survey of cochlear implant recipients was conducted to study how implants may impact people at work. Using a self-reporting questionnaire, recipients using four cochlear implant designs were surveyed about spoken communication on the job, overall job performance, job satisfaction, confidence in job retention and in seeking new employment, job promotion, and income. Of the implant recipients using their implants at work (106 people), the majority used their implants during all work hours and reported positive changes in their job situations. The survey results suggest that cochlear implants may help in mitigating functional limitations in the workplace resulting from profound hearing loss

Extensions of tempered representations

Let $\pi, \pi'$ be irreducible tempered representations of an affine Hecke algebra H with positive parameters. We compute the higher extension groups $Ext_H^n (\pi,\pi')$ explicitly in terms of the representations of analytic R-groups corresponding to $\pi$ and $\pi'$. The result has immediate applications to the computation of the Euler-Poincar\'e pairing $EP(\pi,\pi')$, the alternating sum of the dimensions of the Ext-groups. The resulting formula for $EP(\pi,\pi')$ is equal to Arthur's formula for the elliptic pairing of tempered characters in the setting of reductive p-adic groups. Our proof applies equally well to affine Hecke algebras and to reductive groups over non-archimedean local fields of arbitrary characteristic. This sheds new light on the formula of Arthur and gives a new proof of Kazhdan's orthogonality conjecture for the Euler-Poincar\'e pairing of admissible characters.Comment: This paper grew out of "A formula of Arthur and affine Hecke algebras" (arXiv:1011.0679). In the second version some minor points were improve

Neutron experiments at Portsmouth for measuring flow and {sup 235}U content in UF{sub 6} gas

The Portsmouth Gaseous Diffusion Plant produces enriched uranium for use in commercial power reactors. The plant also aids disposal of excess high-enrichment uranium (HEU) by blending it with lower-enrichment material. Experiments were conducted to test two neutron-based methods for monitoring the down-blending of HEU. Results of the initial experiments showed that gas (on-off) could be detected, but that additional tests and data are needed to quantify the flow velocity and {sup 235}U content. The experiments used a {sup 252}Cf neutron source to induce fission in a small fraction of the {sup 235}U contained in the UF{sub 6} gas. The first method measured the attenuation of neutrons passing through the low-pressure UF{sub 6} gas in a 7.6-cm diameter pipe. The concept was based on the fact that some of the thermal neutrons are absorbed by {sup 235}U, thus changing the observed count rate. The second method, tested on a 20-cm diameter pipe where gas pressure was higher, used a modulated neutron flux to induce fission in the {sup 235}U. Modulation was achieved by moving a neutron source. During both experiments, plant monitoring equipment showed that light gases (freon, oxygen, and nitrogen) were present in widely varying amounts, along with the UF{sub 6} gas. These gases may have affected the experimental results, at least to the extent that they replaced UF{sub 6}. This report also contains results of computer simulations and tests performed on the electronics after the experiments were completed at Portsmouth. Recommendations are made for follow-on work to measure the flow velocity and {sup 235}U content