Enthalpy changes in the formation of the proton electrochemical potential and its components

Enthalpy changes in the formation of a proton electrochemical potential (Delta mu H+) and its components, DeltapH (proton gradient) and Deltapsi (electrical potential), across two types of E. coli membrane vesicles were investigated. Flow dialysis experiments showed that in 0.1 M KPi, pH 6.6, E. coli GR19N membrane vesicles coupled with d-lactate exhibited 57 mV for DeltapH, 70 mV for Deltapsi, and 127 mV for Delta mu H+. Microcalorimetric measurements revealed that the corresponding enthalpy changes (DeltaH(pH), DeltaH(psi) and DeltaHm) were 3.5, 3.3 and 6.9 kcal/mole, respectively. Moreover, in E. coli ML 308-225 membrane vesicles across which 120mV of Delta mu H+ was generated, values of DeltaH(pH) and DeltaH(psi) were determined as 7.0 and 6.6 kcal/mole, as compared with the previously reported 14.1 kcal/mole for DeltaH(m). Comparisons of these enthalpy data revealed that component enthalpies (DeltaH(pH) and DeltaH(psi)) essentially added up to the total enthalpy (DeltaHm), providing a self-consistent test for the obtained data. In both membranes, the ratio ofDeltaH(psi) to Deltapsi was comparable to that of DeltaH(pH) to DeltapH in the formation of Delta mu H+. These observations indicated that the process of the movement of H+ across the membranes was the major contributor to the observed energetic changes. Moreover, the enthalpy change in the formation of Delta mu H+ was compared with the membranes derived from GR19N and ML 308-225 and coupled with NADH and d-lactate. The results were discussed in terms of trans-membrane phenomena.     

A novel rectangular airlift reactor with mesh baffle-plates

An experimental rectangular airlift reactor having mesh baffle-plates has been fabricated out of Perspex and compared with conventional airlift and bubble column in terms of gas holdup, volumetric mass transfer coefficient and mixing time. Mesh baffle-plates improved mass transfer and mixing with the mass transfer coefficient of the proposed reactor being up to 12% higher than that in a conventional airlift reactor under the same operating condition. The mixing time of the proposed reactor can be 95% lower than that of the airlift reactor.     

Fermentation of corn fibre sugars by an engineered xylose utilizing Saccharomyces yeast strain

The ability of a recombinant Saccharomyces yeast strain to ferment the sugars glucose, xylose, arabinose and galactose which are the predominant monosaccharides found in corn fibre hydrolysates has been examined. Saccharomyces strain 1400 (pLNH32) was genetically engineered to ferment xylose by expressing genes encoding a xylose reductase, a xylitol dehydrogenase and a xylulose kinase. The recombinant efficiently fermented xylose alone or in the presence of glucose. Xylose-grown cultures had very little difference in xylitol accumulation, with only 4 to 5g/l accumulating, in aerobic, micro-aerated and anaerobic conditions. Highest production of ethanol with all sugars was achieved under anaerobic conditions. From a mixture of glucose (80g/l) and xylose (40g/l), this strain produced 52g/l ethanol, equivalent to 85% of theoretical yield, in less than 24h. Using a mixture of glucose (31g/l), xylose (15.2g/l), arabinose (10.5g/l) and galactose (2g/l), all of the sugars except arabinose were consumed in 24h with an accumulation of 22g ethanol/l, a 90% yield (excluding the arabinose in the calculation since it is not fermented). Approximately 98% theoretical yield, or 21g ethanol/l, was achieved using an enzymatic hydrolysate of ammonia fibre exploded corn fibre containing an estimated 47.0g mixed sugars/l. In all mixed sugar fermentations, less than 25% arabinose was consumed and converted into arabitol.     

Design, synthesis, expression, and characterization of the genes for mouse Fc gamma RIIb1 and Fc gamma RIIb2 cytoplasmic regions.

The cytoplasmic regions of the mouse low-affinity Fc gamma RII isoforms, mFc gamma RIIb1, and mFc gamma RIIb2, play a key role in signal transduction by mediating different cellular functions. mFc gamma RIIb1 has a 94-residue cytoplasmic region, whereas mFc gamma RIIb2 has a 47-residue cytoplasmic region. Genes encoding the cytoplasmic regions of mFc gamma RIIb1 (b1-94) and mFc gamma RIIb2 (b2-47) were designed, synthesized, and expressed as fusion proteins in Escherichia coli. A sequence-specific protease, thrombin, was used to release the b1-94 peptide, which was purified by using HPLC. The b2-47 peptide was synthesized chemically. CD spectropolarimetry was employed to examine the secondary structures of b1-94 and b2-47. These studies were conducted in aqueous solution, in mixtures of water and trifluoroethanol or methanol, and as a function of temperature. The results indicate that the b1-94 and b2-47 structures are sensitive functions of the solvent environment, and that nonaqueous solvents induce significant alpha-helical structure.