Energy, carbon dioxide and water use implications of hydrous ethanol production

Sub-azeotropic hydrous ethanol has been demonstrated as an effective diesel fuel replacement when used in dual-fuel compression ignition engines. Previous studies have also suggested that hydrous ethanol may be more efficient to produce from corn than anhydrous ethanol. In this study, we investigate corn ethanol production from a dry-mill, natural gas-fired corn ethanol refinery, producing ethanol with a range of ethanol concentrations from 58°wt% - 100°wt% to determine the effect on energy use, water consumption and greenhouse gas (GHG) emissions in the refining stage of the corn ethanol lifecycle. A second law (exergy) analysis of anhydrous ethanol refining revealed the overall process to be 70% efficient, whereby 86% of the exergy losses could be accounted for by three processes: fermentation (34%), steam generation (29%) and distiller’s grains and solubles drying (23%). We found that producing 86°wt% ethanol is optimal as thermal energy consumption decreases by a maximum of 10% (from 7.7°MJ/L to 6.9°MJ/L). These savings have the potential to reduce energy costs by approximately 8% ($0.34 /L) and reduce refinery emissions by 8% (2°g°CO_2e/MJ). Production of hydrous ethanol reduced refinery water use due to decreased evaporative losses in the cooling towers, leading to water savings of between 3 - 6% at 86°wt% ethanol.This work was supported in part by the Minnesota Corn Growers Association under contract number 1051-14EU and St Edmund’s College (Cambridge, United Kingdom).This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.enconman.2015.08.03

Catalytic Water Co-Existing with a Product Peptide in the Active Site of HIV-1 Protease Revealed by X-Ray Structure Analysis

BACKGROUND: It is known that HIV-1 protease is an important target for design of antiviral compounds in the treatment of Acquired Immuno Deficiency Syndrome (AIDS). In this context, understanding the catalytic mechanism of the enzyme is of crucial importance as transition state structure directs inhibitor design. Most mechanistic proposals invoke nucleophilic attack on the scissile peptide bond by a water molecule. But such a water molecule coexisting with any ligand in the active site has not been found so far in the crystal structures. PRINCIPAL FINDINGS: We report here the first observation of the coexistence in the active site, of a water molecule WAT1, along with the carboxyl terminal product (Q product) peptide. The product peptide has been generated in situ through cleavage of the full-length substrate. The N-terminal product (P product) has diffused out and is replaced by a set of water molecules while the Q product is still held in the active site through hydrogen bonds. The position of WAT1, which hydrogen bonds to both the catalytic aspartates, is different from when there is no substrate bound in the active site. We propose WAT1 to be the position from where catalytic water attacks the scissile peptide bond. Comparison of structures of HIV-1 protease complexed with the same oligopeptide substrate, but at pH 2.0 and at pH 7.0 shows interesting changes in the conformation and hydrogen bonding interactions from the catalytic aspartates. CONCLUSIONS/SIGNIFICANCE: The structure is suggestive of the repositioning, during substrate binding, of the catalytic water for activation and subsequent nucleophilic attack. The structure could be a snap shot of the enzyme active site primed for the next round of catalysis. This structure further suggests that to achieve the goal of designing inhibitors mimicking the transition-state, the hydrogen-bonding pattern between WAT1 and the enzyme should be replicated

The hepatitis B virus X protein activates nuclear factor of activated T cells (NF-AT) by a cyclosporin A-sensitive pathway.

The X gene product of the human hepatitis B virus (HBx) is a transcriptional activator of various viral and cellular genes. We recently have determined that the production of tumor necrosis factor-alpha (TNF-alpha) by HBV-infected hepatocytes is transcriptionally up-regulated by HBx, involving nuclear factor of activated T cells (NF-AT)-dependent activation of the TNF-alpha gene promoter. Here we show that HBx activates NF-AT by a cyclosporin A-sensitive mechanism involving dephosphorylation and nuclear translocation of the transcription factor. Luciferase gene expression assays demonstrated that HBx transactivates transcription through NF-AT-binding sites and activates a Gal4-NF-AT chimeric protein. DNA-protein interaction assays revealed that HBx induces the formation of NF-AT-containing DNA-binding complexes. Immunofluorescence analysis demonstrated that HBx induces the nuclear translocation of NF-AT, which can be blocked by the immunosuppressive drug cyclosporin A. Furthermore, immunoblot analysis showed that the HBx-induced activation and translocation of NF-AT are associated with its dephosphorylation. Thus, HBx may play a relevant role in the intrahepatic inflammatory processes by inducing locally the expression of cytokines that are regulated by NF-AT

Mechanistic evidence for a front-side, SNi-type reaction in a retaining glycosyltransferase

A previously determined crystal structure of the ternary complex of trehalose-6-phosphate synthase identified a putative transition state–like arrangement based on validoxylamine A 6?-O-phosphate and uridine diphosphate in the active site. Here linear free energy relationships confirm that these inhibitors are synergistic transition state mimics, supporting front-face nucleophilic attack involving hydrogen bonding between leaving group and nucleophile. Kinetic isotope effects indicate a highly dissociative oxocarbenium ion–like transition state. Leaving group 18O effects identified isotopically sensitive bond cleavages and support the existence of a hydrogen bond between the nucleophile and departing group. Brønsted analysis of nucleophiles and Taft analysis highlight participation of the nucleophile in the transition state, also consistent with a front-face mechanism. Together, these comprehensive, quantitative data substantiate this unusual enzymatic reaction mechanism. Its discovery should prompt useful reassessment of many biocatalysts and their substrates and inhibitor

The recycling of carbon in glucose, lactate and alanine in sheep

Pregnant ewes with catheters implanted in an artery and the uterine and recurrent tarsal veins were infused at a constant rate with U−¹⁴C-labelled glucose, alanine or bicarbonate. Measurements were made of the overall and local fractional contribution of glucose and alanine to CO₂ production and of the extent of interconversion of these metabolites. In the whole animal, by coupling the results with the authors’ previous study of lactate metabolism, a solution was obtained to an open unrestricted 4-compartment model of the exchange of carbon between glucose, lactate, alanine and CO₂. A more limited study was made with non-pregnant sheep because complete data for lactate interactions with alanine were not available. Our analysis of glucose/lactate/alanine/CO₂ interactions in pregnant sheep suggests that about two-thirds of the glycogenic carbon was oxidised fairly directly to CO₂. There was relatively little recycling of glucose carbon through lactate and alanine so that most of the remaining glycogenic carbon was stored as product with relatively long turnover time. It is possible that much of this was in the form of muscle glycogen, and analysis of glycogenic carbon exchange across the hind limb muscle was consistent with this conclusion. In non-pregnant ewes, the findings, although incomplete, suggested that there were no great differences from the findings in pregnant ewes.Derek B. Lindsay, Patrick J. Barker, Andrew J. Northrop, Brian P. Setchell, Graham J. Faichne