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Long-term phosphorus (P) applications can increase soil P concentrations in excess of agronomic optima, posing a risk to water quality. Once fertilization stops, however, it may take time for soil P concentrations to decline. Whereas P fertilization adds orthophosphate, little is known about changes in other soil P forms during P buildup and drawdown. This study examined changes in P pools (total P, Olsen P, Mehlich P, and water-extractable P) and P forms determined by 31P-nuclear magnetic resonance spectroscopy (P-NMR) in grazed grassland plots from Northern Ireland. Between 1994 and 1999, all plots received 8.3 kg P ha-1 yr-1 with variable rates of nitrogen (100-500 kg N ha-1 yr-1). From 2000 to 2005, plots received 0, 20, 40, or 80 kg P ha-1 yr-1 and 250 kg N ha-1 yr-1; from 2005 to 2010, no P fertilizer was applied to any plots. In 2005, soil P pool concentrations at the highest P fertilization rates were significantly elevated compared with those in 2000 but had decreased to 2000 concentrations by 2010. In soils receiving no P, soil P pool concentrations were significantly lower than those in 1994 only in 2010. There were few changes in P forms determined by P-NMR. Orthophosphate followed the same trend observed for the soil P pools; total organic P, total inositol phosphates, and total orthophosphate monoesters and diesters were highest in 2010 in the soil receiving no P fertilizer for 10 yr. For these soils, fertilizer application and cessation influenced inorganic P more than organic P. [ABSTRACT FROM AUTHOR]

Phosphorus stratification leaves high P concentrations at the soil surface, which are vulnerable to loss in runoff. Understanding P forms at the soil surface may help control P loss, but little information is available on how P forms stratify in soils. We used 31P nuclear magnetic resonance (NMR) spectroscopy and chemical analysis to characterize P forms and the elements controlling P cycling in Cecil soil (a fine, kaolinitic, thermic Typic Kanhapludult) that became P stratified after 11 yr of cropping management conducted under combinations of tillage (conventional and no-till, CT and NT, respectively) and inorganic chemical (CF) and poultry litter (PL) fertilization. Samples from three soil depths (0-2.5, 2.5-5, and 5-15 cm) were sequentially extracted in NaOH-ethylenediaminetetraacetic acid (EDTA) and HCl before 31P-NMR spectroscopy. The NaOH-EDTA extraction recovered 63 to 83% of the total P in a range of P forms, and HCl recovered 2 to 16% of the total P, mainly orthophosphate. Phosphorus forms and concentrations were evenly distributed in soil layers only in the CT treatment with CF. Stratification of orthophosphate and phytate occurred in NT samples fertilized with PL and CF, with the highest concentrations in the top 2.5 cm. Increased orthophosphate and phytate concentrations were detected at the soil surface for CT-PL samples, indicating that PL is not as well mixed by tillage as CF. These results suggest that P fertilizers should be placed below the soil surface under NT to avoid stratification and thus reduce potential P loss in surface runoff. [ABSTRACT FROM AUTHOR]

Phosphorus nuclear magnetic resonance (31P NMR) spectroscopy is an important tool for the study of soil P and has significantly advanced our knowledge of soil P forms, particularly organic P; however, it must be used correctly to provide meaningful results. This review covers the 31P NMR studies of soil published from 2005 to 2013. The first part discusses preparing samples for 31P NMR, including extractants, pre- and post-extraction treatments, the physical state of the soil sample at the time of extraction, extraction length, the soil/extractant ratio, P recovery, P in residues, methods to concentrate extracts, redissolving samples for 31P NMR experiments, the use of the internal standard methylene diphosphonic acid, and the potential for degradation with any of these steps. The second part of this review focuses on NMR experiment parameters, including delay times, proton decoupling, and experiment length. Potential concerns in these areas are noted, and suggestions are given for procedures to optimize the information obtained from a 31P NMR experiment. [ABSTRACT FROM AUTHOR]

In the Lake Champlain Basin, phosphorus (P) loading from streambank erosion and cropland are both important P sources, and a better understanding of the factors affecting riparian P loss is needed to help prioritize riparian restoration efforts. We utilized solution phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy and an enzyme hydrolysis method to characterize P and assess bioavailability in 14 commonly mapped riparian soils from northwestern Vermont. Surface horizons were sampled from distinct series at two riparian restoration sites to capture a range of soil properties. Samples were extracted with sodium hydroxide-ethylenediaminetetra-acetic acid (NaOH-EDTA) and analyzed by solution 31P NMR to speciate and quantify P compounds, and commercially available phosphatase enzymes were used to fractionate water-extractable molybdate unreactive P (MUP) into labile orthophosphate monoesters and orthophosphate diesters. Phosphorus extracted by NaOH-EDTA ranged from 74 to 510 mg P kg-1 (representing 14.2 to 31.9% of total soil P), of which 58 ± 13% was identified as organic P. Phosphorus compounds identified in all samples included myo-inositol hexakisphosphate (myo-IHP), scyllo-IHP, neo-IHP, chir-IHP, glycerophosphate, glucose 6-phosphate, mononucleotides, choline phosphate, glucose 1-phosphate, DNA, pyrophosphate, and orthophosphate. Orthophosphate monoesters accounted for 53.7 ± 12.3% of total NaOH-EDTA extractable P and 93 ± 3% of the NaOH-EDTA organic P, indicating the importance of organic P in these soils. Stereoisomers of IHP accounted for 29 ± 7% of NaOH-EDTA extractable Po. For the water extractions, 78 ± 13% of total P was MUP, of which 18 ± 6% was labile orthophosphate monoesters and 31 ± 15% was orthophosphate diesters. Results suggest that analytical indices of riparian P loss potential should consider both organic and inorganic P. [ABSTRACT FROM AUTHOR]

The assembly-line architecture of polyketide synthases (PKSs) provides an opportunity to rationally reprogram polyketide biosynthetic pathways to produce novel antibiotics. A fundamental challenge toward this goal is to identify the factors that control the unidirectional channeling of reactive biosynthetic intermediates through these enzymatic assembly lines. Within the catalytic cycle of every PKS module, the acyl carrier protein (ACP) first collaborates with the ketosynthase (KS) domain of the paired subunit in its own homodimeric module so as to elongate the growing polyketide chain and then with the KS domain of the next module to translocate the newly elongated polyketide chain. Using NMR spectroscopy, we investigated the features of a structurally characterized ACP domain of the 6-deoxyerythronolide B synthase that contribute to its association with its KS translocation partner. Not only were we able to visualize selective protein-protein interactions between the two partners, but also we detected a significant influence of the acyl chain substrate on this interaction. A novel reagent, CF-S-ACP, was developed as a F NMR spectroscopic probe of protein-protein interactions. The implications of our findings for understanding intermodular chain translocation are discussed. [ABSTRACT FROM AUTHOR]

The article discusses the study which compares the phophorus (P) stratification forms in no till soils to plowed soils using P Nuclear Magnetic Resonance (NMR) from the Prince Edward Island in Canada. It indicates that phosphorus stratification for no till soils may be due to factors like lack of mixing when applying fertilizers in the soil or through the direct decomposition of decaying organic matter. The study implies that lack of mixing may contribute to phosphorus startification but increases the potential for P loss in agricultural runoffs.

The CLC ‘Cl− channel’ family consists of both Cl−/H+ antiporters and Cl− channels. Although CLC channels can undergo large, conformational changes involving cooperativity between the two protein subunits, it has been hypothesized that conformational changes in the antiporters may be limited to small movements localized near the Cl− permeation pathway. However, to date few studies have directly addressed this issue, and therefore little is known about the molecular movements that underlie CLC-mediated antiport. The crystal structure of the Escherichia coli antiporter ClC-ec1 provides an invaluable molecular framework, but this static picture alone cannot depict the protein movements that must occur during ion transport. In this study we use fluorine nuclear magnetic resonance (NMR) to monitor substrate-induced conformational changes in ClC-ec1. Using mutational analysis, we show that substrate-dependent 19F spectral changes reflect functionally relevant protein movement occurring at the ClC-ec1 dimer interface. Our results show that conformational change in CLC antiporters is not restricted to the Cl− permeation pathway and show the usefulness of 19F NMR for studying conformational changes in membrane proteins of known structure. [ABSTRACT FROM AUTHOR]

Polyketides are a medicinally important class of natural products. The architecture of modular polyketide synthases (PKSs), composed of multiple covalently linked domains grouped into modules, provides an attractive framework for engineering novel polyketide-producing assemblies. However, impaired domain-domain interactions can compromise the efficiency of engineered polyketide biosynthesis. To facilitate the study of these domain-domain interactions, we have used nuclear magnetic resonance (NMR) spectroscopy to determine the first solution structure of an acyl carrier protein (ACP) domain from a modular PKS, 6-deoxyerythronolide B synthase (DEBS). The tertiary fold of this 10-kD domain is a three-helical bundle; an additional short helix in the second loop also contributes to the core helical packing. Superposition of residues 14-94 of the ensemble on the mean structure yields an average atomic RMSD of 0.64 ± 0.09 Å for the backbone atoms (1.21 ± 0.13 Å for all non-hydrogen atoms). The three major helices superimpose with a backbone RMSD of 0.48 ± 0.10 Å (0.99 ± 0.11 Å for non-hydrogen atoms). Based on this solution structure, homology models were constructed for five other DEBS ACP domains. Comparison of their steric and electrostatic surfaces at the putative interaction interface (centered on helix II) suggests a model for protein-protein recognition of ACP domains, consistent with the previously observed specificity. Site-directed mutagenesis experiments indicate that two of the identified residues influence the specificity of ACP recognition. [ABSTRACT FROM AUTHOR]