Resonance Raman Spectroscopy Reveals pH-Dependent Active Site Structural Changes of Lactoperoxidase Compound 0 and Its Ferryl Heme O–O Bond Cleavage Products

The first step in the enzymatic cycle of mammalian peroxidases, including lactoperoxidase (LPO), is binding of hydrogen peroxide to the ferric resting state to form a ferric-hydroperoxo intermediate designated as Compound 0, the residual proton temporarily associating with the distal pocket His109 residue. Upon delivery of this “stored” proton to the hydroperoxo fragment, it rapidly undergoes O–O bond cleavage, thereby thwarting efforts to trap it using rapid mixing methods. Fortunately, as shown herein, both the peroxo and the hydroperoxo (Compound 0) forms of LPO can be trapped by cryoradiolysis, with acquisition of their resonance Raman (rR) spectra now permitting structural characterization of their key Fe–O–O fragments. Studies were conducted under both acidic and alkaline conditions, revealing pH-dependent differences in relative populations of these intermediates. Furthermore, upon annealing, the low pH samples convert to two forms of a ferryl heme O–O bond-cleavage product, whose ν(Fe═O) frequencies reflect substantially different Fe═O bond strengths. In the process of conducting these studies, rR structural characterization of the dioxygen adduct of LPO, commonly called Compound III, has also been completed, demonstrating a substantial difference in the strengths of the Fe–O linkage of the Fe–O–O fragment under acidic and alkaline conditions, an effect most reasonably attributed to a corresponding weakening of the trans-axial histidyl imidazole linkage at lower pH. Collectively, these new results provide important insight into the impact of pH on the disposition of the key Fe–O–O and Fe═O fragments of intermediates that arise in the enzymatic cycles of LPO, other mammalian peroxidases, and related proteins

Design and Synthesis of Oxazoline-Based Scaffolds for Hybrid Lewis Acid/Lewis Base Catalysis of Carbon–Carbon Bond Formation

A new class of hybrid Lewis acid/Lewis base catalysts has been designed and prepared with an initial objective of promoting stereoselective direct aldol reactions. Several scaffolds were synthesized that contain amine moieties capable of enamine catalysis, connected to heterocyclic metal-chelating sections composed of an oxazole–oxazoline or thiazole–oxazoline. Early screening results have identified oxa­zole–oxazoline-based systems capable of promoting a highly diastereo- and enantioselective direct aldol reaction of propionaldehyde with 4-nitrobenzaldehyde, when combined with Lewis acids such as zinc triflate

Sequential Grazing Systems for Beef Cattle Production

Pasture productivity in Iowa is often limited by low productivity of cool-season grasses during summer. This uneven seasonal distribution of for age production could be improved by including species in pasture systems that perform better under higher temperatures. Warm-season grasses produce most of their growth during summer when cool-season grasses are semi -dormant. By using cool-season and warm-season pastures in a sequential system it should be possible to improve seasonal productivity. The overall objective of this project i s to evaluate the productivity of sequential grazing system s for beef cattle production in Southern Iowa. Specific objectives are to: 1) evaluate the impact of legumes on the productivity of cool-season pastures grazed in the spring and fall, 2) evaluate warm-season grasses f or summer grazing, and 3) determine the effects of pasture sequence on the productivity of season-long grazing systems

Sequential Grazing of Cool- and Warm-Season Pastures

Pasture productivity in Iowa often is limited by low productivity of cool-season grasses during summer. This uneven seasonal distribution of forage production could be improved by including species in pasture systems that perform better under higher temperatures. Warm-season grasses produce most of their growth during summer when cool-season grasses are semi-dormant. By using cool-season and warm-season pastures in a sequential system, it should be possible to improve seasonal productivity

Sequential Grazing Systems for Beef Cattle Production

Pasture productivity in Iowa is often limited by low productivity of cool-season grasses during summer. This uneven seasonal distribution of for age production could be improved by including species in pasture systems that perform better under higher temperatures. Warm-season grasses produce most of their growth during summer when cool-season grasses are semi -dormant. By using cool-season and warm-season pastures in a sequential system it should be possible to improve seasonal productivity. The overall objective of this project i s to evaluate the productivity of sequential grazing system s for beef cattle production in Southern Iowa. Specific objectives are to: 1) evaluate the impact of legumes on the productivity of cool-season pastures grazed in the spring and fall, 2) evaluate warm-season grasses f or summer grazing, and 3) determine the effects of pasture sequence on the productivity of season-long grazing systems.</p

Sequential Grazing of Cool- and Warm-Season Pastures

Pasture productivity in Iowa often is limited by low productivity of cool-season grasses during summer. This uneven seasonal distribution of forage production could be improved by including species in pasture systems that perform better under higher temperatures. Warm-season grasses produce most of their growth during summer when cool-season grasses are semi-dormant. By using cool-season and warm-season pastures in a sequential system, it should be possible to improve seasonal productivity.</p