Christopher S. Jones

Current trends in molecular recognition and bioseparation

Molecular recognition guides the selective interaction of macromolecules with each other in essentially all biological processes. Perhaps the most impactful use of biomolecular recognition in separation science has been in affinity chromatography. The results of the last 26 years, since Cuatrecases, Wilchek and Anfinsen first reported the purification of staphylococcal nuclease, have validated the power of biomolecular specificity for purification. This power has stimulated an explosion of solid-phase ligand designs and affinity chromatographic applications. An ongoing case in point is the purification of recombinant proteins, which has been aided by engineering the proteins to contain Affinity-Tag sequences, such as hexa-histidine for metal-chelate separation and epitope sequence for separation by an immobilized monoclonal antibody. Tag technology can be adapted for plate assays and other solid-phase techniques. The advance of affinity chromatography also has stimulated immobilized ligand-based methods to characterize macromolecular recognition, including both chromatographic and optical biosensor methods. And, new methods such as phage display and other diversity library approaches continue to emerge to identify new recognition molecules of potential use as affinity ligands. Overall, it is tantalizing to envision a continued evolution of new affinity technologies which use the selectivity built into biomolecular recognition as a vehicle for purification, analysis, screening and other applications in separation sciences.

Nitrate-Nitrogen Export: Magnitude and Patterns from Drainage Districts to Downstream River Basins

Alteration of the prairie pothole ecosystem through installation of subsurface tile drains has enabled the U.S. Corn Belt to become one of the most agriculturally productive areas in the world but has also led to increased nitrogen losses to surface water. The literature contains numerous field plot studies but few in-depth studies of nitrate exports from small, tile-drained catchments representative of agricultural drainage districts. The objectives of this study were to quantify hydrology and nitrate-nitrogen (NO-N) export patterns from three tile-drained catchments and the downstream river over a 5-yr period, compare results to prior plot-, field-, and watershed-scale studies, and discuss implications for water quality improvement in these landscapes. The tile-drained catchments had an annual average water yield of 247 mm yr, a flow-weighted NO-N concentration of 17.1 mg L, and an average NO-N loss of nearly 40 kg ha yr. Overall, water yields were consistent with prior tile drainage studies in Iowa and the upper Midwest, but associated NO-N concentrations and losses were among the highest reported for plot studies and higher than those found in small watersheds. More than 97% of the nitrate export occurs during the highest 50% of flows, at both the small catchment and river basin scale. Findings solidified the importance of working at the drainage district scale to achieve nitrate reductions necessary to meet water quality goals. They also point to the need for implementing strategies that address both hydrology and nitrogen supply in tile-drained landscapes.

From agricultural intensification to conservation: sediment transport in the Raccoon River, Iowa, 1916-2009.

Fluvial sediment is a ubiquitous pollutant that negatively affects surface water quality and municipal water supply treatment. As part of its routine water supply monitoring, the Des Moines Water Works (DMWW) has been measuring turbidity daily in the Raccoon River since 1916. For this study, we calibrated daily turbidity readings to modern total suspended solid (TSS) concentrations to develop an estimation of daily sediment concentrations in the river from 1916 to 2009. Our objectives were to evaluate long-term TSS patterns and trends, and relate these to changes in climate, land use, and agricultural practices that occurred during the 93-yr monitoring period. Results showed that while TSS concentrations and estimated sediment loads varied greatly from year to year, TSS concentrations were much greater in the early 20th century despite drier conditions and less discharge, and declined throughout the century. Against a backdrop of increasing discharge in the Raccoon River and widespread agricultural adaptations by farmers, sediment loads increased and peaked in the early 1970s, and then have slowly declined or remained steady throughout the 1980s to present. With annual sediment load concentrated during extreme events in the spring and early summer, continued sediment reductions in the Raccoon River watershed should be focused on conservation practices to reduce rainfall impacts and sediment mobilization. Overall, results from this study suggest that efforts to reduce sediment load from the watershed appear to be working.

Crop rotation and Raccoon River nitrate

Previous research predicted that the biofuel-driven expansion of corn (Zea mays L.) area would increase riverine export of nitrate-nitrogen (NO3-N) in the Mississippi River Basin. Accurate information about water quality trends in agricultural watersheds is needed to better inform agricultural policy and to help quantify the effectiveness of field and landscape management practices. This study was designed to (1) characterize possible NO3-N trends within the Raccoon River watershed (RRWS) of central Iowa, and (2) explore links between the relative areas planted to corn and soybean (Glycine max) and water quality. We examined NO3-N concentration and loading data from more than 60 main stem river and tributary locations in the RRWS for the period 1999 to 2014. In addition, we assessed the role of climate, crop rotations, and simplified annual N budgets on NO3-N concentrations and loads to show that expansion of corn area has not increased Raccoon River NO3-N levels. Nitrate-N concentrations have not increased as corn area increased 19% and fertilizer N inputs increased 24% since 1999. We conclude that expansion of corn area at the expense of soybean may be affecting water quality. Better management of soybean in a corn–soybean rotation should reduce NO3-N export from the watershed, and reducing throughput of water in this artificially drained system will improve water quality.

Evaluating energetics of erythropoietin ligand binding to homodimerized receptor extracellular domains

Abstract A number of techniques have been employed to characterize the energetics of EPO-EPOR-Fc interactions. AUC studies have shown that EPO and EPOR-Fc exist as monomers at concentrations less that 10 μM. Under these conditions, EPO and the EPOR-Fc associate to form a 1:1 complex and this complex does not undergo any further assembly processes. Studies in which the biological activity of EPO at a cell surface is competed by free and dimerized receptor show that the dimerized receptor is 750-fold more potent. This suggests that EPO is bound by both receptor subunits on the Fc chimera, as shown in Fig. 9D. This assembly model provides a foundation for interpretation of the kinetic, thermodynamic, and spectral results. SPR kinetic analyses of the EPO-EPOR-Fc interaction yields association and dissociation rate constants of 8.0 × 10 7 M −1 sec −1 and 2.4 × 10 −4 sec −1 , respectively, for an overall affinity of 3 p M (see Fig. 12). The half-maximal response in a cellular proliferation assay is evoked at an EPO concentration of 10 p M , 54 which is similar to the affinity kinetically determined for the EPOR-Fc. This value suggests that the EPOR-Fc chimera may be a reasonable model for the receptor on a cell surface (see Fig. 17). The use of this reagent is also supported by the studies of Remy et al. , who demonstrate that the EPOR is likely to exist as a dimer on the cell surface, in the absence of ligand. Titration calorimetry confirms the 1:1 stoichiometry, observed by AUC and SPR approaches. Further, the temperature dependence of the enthalpy yields a heat capacity that can be interpreted in terms of a large conformational change in the EPOR on EPO binding. Comparing the structures of the free and complexed receptor, some conformational changes are noted in loops L3 and L6. 18 However, these changes are small compared with the conformational changes predicted from an analysis of the calorimetric data reported here, i.e., equivalent to the folding of ∼70 amino acids. The change in buried surface area between the free and complexed EPOR, determined from structural data, is also quite small when compared with the predicted value of 7500 A 2 from calorimetry. Further studies need to be done to rationalize these observations. These may include an attempt to determine if conformational changes are communicated to the Fc domain and the extent to which EPOR extracellular domains are oriented on the Fc domain in a manner that faithfully reflects their orientation on a cell surface. Finally, while changes in the CD spectra are observed on binding of EPO to the EPOR-Fc, and the monomeric receptor, these changes may be due to subtle changes in the microenvironments of tryptophans and tyrosines and do not require conformational changes of the magnitude suggested from the calorimetry results. In summary, to define macromolecular interactions in solution, the stoichiometry, thermodynamics, and kinetics of assembly need to be understood. This task requires that a multitechnology approach be implemented. Here, AUC established an assembly model and provided a foundation on which SPR, ITC, and CD studies could be based and from which interpretation of these data could be extended. SPR established that the affinity of the dimerized receptor was high and ITC suggested that there may be a significant conformational change on binding. CD suggested that observed spectral changes may be due to these presumed conformational changes, but would also be consistent with more subtle changes. These studies further demonstrate that the EPOR-Fc is a valid model for the dimerized receptor on the cell surface and, as such, will be a useful tool for probing the differences in the interactions of the receptor dimer with EPO agonists and antogonists.

How Paired Is Paired? Comparing Nitrate Concentrations in Three Iowa Drainage Districts

Quantifying the effectiveness of perceived best management practices (BMPs) at the field and landscape-scale is difficult, so paired watershed studies are used to detect water quality improvements. We evaluated concentrations of NO-N discharged from three tiled Iowa watersheds during a 4-yr period to assess their suitability for a paired watershed approach. Our objectives were to evaluate similarities in physical characteristics, concentration patterns, and correlation among the three paired sites and perform a minimum detectable change (MDC) analysis on paired site configurations. The study results demonstrate that concentration variability within and between sample sites affected correlation among the paired basins, even though the physical characteristics of the basins are quite similar. Restricting comparisons to the active tile drainage period (March-July) improved correlations. The lack of a suitable correlation will impair the ability to detect changes expected to result from BMP implementation. The MDC for NO-N concentration change detection varied from 6.9 to 12.9% and averaged 8% for the best control-treatment pair. To ensure that conservation resources are being used effectively, implemented BMPs should focus on practices capable of achieving at least this magnitude of change. These practices may include reduced fertilizer applications, adoption of cover crops, and land use change.

Use Alkalinity Monitoring to Optimize Bioreactor Performance.

In recent years, the agricultural community has reduced flow of nitrogen from farmed landscapes to stream networks through the use of woodchip denitrification bioreactors. Although deployment of this practice is becoming more common to treat high-nitrate water from agricultural drainage pipes, information about bioreactor management strategies is sparse. This study focuses on the use of water monitoring, and especially the use of alkalinity monitoring, in five Iowa woodchip bioreactors to provide insights into and to help manage bioreactor chemistry in ways that will produce desirable outcomes. Results reported here for the five bioreactors show average annual nitrate load reductions between 50 and 80%, which is acceptable according to established practice standards. Alkalinity data, however, imply that nitrous oxide formation may have regularly occurred in at least three of the bioreactors that are considered to be closed systems. Nitrous oxide measurements of influent and effluent water provide evidence that alkalinity may be an important indicator of bioreactor performance. Bioreactor chemistry can be managed by manipulation of water throughput in ways that produce adequate nitrate removal while preventing undesirable side effects. We conclude that (i) water should be retained for longer periods of time in bioreactors where nitrous oxide formation is indicated, (ii) measuring only nitrate and sulfate concentrations is insufficient for proper bioreactor operation, and (iii) alkalinity monitoring should be implemented into protocols for bioreactor management.

Carbon export from the raccoon river, iowa: patterns, processes, and opportunities.

Farmed landscapes are engineered for productivity, and research suggests they contribute a disproportionate share of inorganic C to the Mississippi River and Gulf of Mexico. Here we use alkalinity and total organic C (TOC) measurements collected from the Raccoon River of Iowa to (i) evaluate inorganic and organic C concentrations and export patterns, (ii) compare current trends to historical conditions, and (iii) link C transport processes to current land use management. Export of inorganic C averaged 106,000 Mg per year and contributes 90% of the C flux from the basin. Alkalinity concentrations are unchanged from 1931 to 1944 levels (∼53 mg L C), but inorganic C loads have doubled due to increasing discharge. Carbonate-rich glacial deposits and agricultural lime provide a large source of inorganic C, and results confirm that alkalinity export in the Raccoon Basin is transport limited. Although fertilization and tillage practices have possibly helped increase C fluxes over the last 70+ yr, the overriding factor on inorganic C export is discharge. Discharge control over C export provides an opportunity for agriculture in terms of quantifying C sequestration for potential C trading. Controlling water flux through soils can limit inorganic C export similar to practices such as reduced tillage and managed rotations.

Mass spectrometric measurements of the negative ions formed in the thermionic ionization detector with nitrogen carrier gas

Abstract A specialized ion source for an atmospheric pressure ionization mass spectrometer was constructed so that ionizing conditions within it were identical to those existing within the nitrogen carrier gas mode of the thermionic ionization detector for gas chromatography. During the passage of several substituted nitrobenzenes through this ion source, an effort was made to identify the negative ions which are thought to be responsible for this detectors response. For all compounds studied no negative ions having masses within the 1–500 a.m.u. mass range of the mass spectrometer were detected. However, negative ions of unknown masses greater than 500 a.m.u. were detected in each case. This unexpected result provides additional basis for speculation concerning the mechanism of response of the thermionic ionization with nitrogen mode.

Variability of nitrate-nitrogen load estimation results will make quantifying load reduction strategies difficult in Iowa

Many states within the Upper Mississippi River Basin are developing strategies to reduce nutrient loads to rivers. Reliable load estimation methods are needed to track progress toward nutrient reduction goals. We evaluated the variability of commonly used interpolation and extrapolation models to estimate nitrate-nitrogen (NO3-N) loads in 11 Iowa rivers. Results showed that the overall consistency between models of annual mean daily loads was low. Differences among the methods were particularly pronounced in May when the greatest NO3-N loads normally occur. The disparity in N load estimation among different methods is troubling given that states, federal agencies, or interest groups must have confidence in NO3-N load estimation procedures if the public is to believe that the load reductions strategies are working.