Production of acetate by mutant strains of Clostridium thermoaceticum

Summary Mutant strains were derived from Clostridium thermoaceticum ATCC 39 289 by treatment with chemical mutagenic agents and selective enrichment procedures. Some mutant strains exhibited growth when cultured in media containing 20 mabetm (1.75 g l^–1) pyruvate of high-magnesium lime (dolime) above pH 6.0. One strain (G-20) grew and produced acetate when 80 mabetm (7 gl^–1) pyruvate or 50 mabetm (2.3 g l^–1) formate at pH 5.6 was the sole energy source. In a fed-batch process controlled at pH 6.2, this mutant produced 52.5 g l^–1 acetate (equivalent to 72.5 g l^–1 Na acetate) and 67 g l^–1 calcium-magnesium acetate (CMA) in 140 h when dolime was the neutralizing agent, with 93% substrate utilization. This mutant strain holds promise for CMA production due to its better tolerance of dolime and its ability to synthesize high levels of acetic acid. Offprint requests to: S. R. Parekh     

Production of glycerol by hansenula anomala

Production of glycerol by Hansenula anomala in molasses-corn steep liquor based media was studied. The accumulation and yield of glycerol was dependent on the medium composition and aeration rate; pH control did not affect the yield. Intermittent addition of sugar during fermentation resulted in significant increase in production of glycerol.     

SO2-catalysed prehydrolysis of coniferous wood for ethanol production

Summary This paper reports studies of large scale, 1500 kg/h, SO₂-catalysed prehydrolysis of coniferous wood chips, samples then being hydrolyzed by a wood-saccharifying enzyme system followed by fermentation to ethanol in the laboratory. Hemicellulose hydrolysis using SO₂ catalyst (prehydrolysis) was found to be more effective than steam alone (autohydrolysis). Prehydrolysis time was 2 min, with steam pressure at 1.2 to 1.7 MPa (175 to 250 psig), and SO₂ catalyst 2.0 to 2.6% on dry wood. The amount of sugars recovered upon enzyme saccharification of the prehydrolysed wood was about 70% of the weight of the wood. When these combined hemicellulose and cellulose sugars were fermented by a pentose-fermenting strain of yeast,Pichia stipitis R, 372 L ethanol/tonne of (dry) wood was obtained.     

Post-translational modification of proteins and the discovery of new medicine

Post-translational modifications are fundamental to processes controlling behaviour, including cellular signaling, growth and transformation. As the molecular basis of protein modifications in normal and disease processes are becoming better defined, so new strategies for designing therapeutic entities to control complex disease processes are emerging.     

On the interaction of tritiated 2-ketobutyrate with 2-keto-3-deoxygluconate-6P aldolase ofPseudomonas putida. Evidence suggesting enzyme-mediated,uncatalyzed tritium exchange

2-Keto-3-deoxygluconate-6P aldolase ofPseudomonas putida mediates exchange between hydrogen isotope at the methylene carbon of 2-ketobutyrate and water. This occurs with aK _m of 20 mM, 100 times the corresponding value for pyruvate, and a V_max approximating 1/710 that of KDPG cleavage. Ketobutyrate is competitive with both pyruvate and 2-keto-3-deoxygluconate-6P for the enzyme. In addition, there is no evidence for C-C synthesis between ketobutyrate andd-glyceraldehyde-3P. A comparison of relativeV/K values for hydrogen exchange shows pyruvate to be 17,600 times better as a substrate than ketobutyrate. The detritiation of [3-³H]ketobutyrate is stereochemically random. In addition, the reaction proceeds with ak _H/k _T isotope effect of 15.3, consistent with C-H bond turnover being rate-determining. The E-ketobutyrate complex is reductively trapped, inactivating the enzyme. Reductive inactivation kinetics of E-ketobutyrate compared to E-pyruvate suggests more of the complex may be partitioned to ketimine in the ketobutyrate case than in the pyruvate case. A mechanism is considered in which ketobutyrate is bound as a ketimine in an orientation such that the active site acid/basic group cannot mediate catalytic ketimine/eneamine interconversion. Thus, exchange would result from hydrogen ionization at C-3′ of the ketimine, a slow spontaneous step compared to overall complex turnover. This noncatalyzed deprotonation would explain dissymmetry in exchange, the poorV/K compared to pyruvate, and a large tritium isotope effect.     

Mean Recency Period for Estimation of HIV-1 Incidence with the BED-Capture EIA and Bio-Rad Avidity in Persons Diagnosed in the United States with Subtype B

HIV incidence estimates are used to monitor HIV-1 infection in the United States. Use of laboratory biomarkers that distinguish recent from longstanding infection to quantify HIV incidence rely on having accurate knowledge of the average time that individuals spend in a transient state of recent infection between seroconversion and reaching a specified biomarker cutoff value. This paper describes five estimation procedures from two general statistical approaches, a survival time approach and an approach that fits binomial models of the probability of being classified as recently infected, as a function of time since seroconversion. We compare these procedures for estimating the mean duration of recent infection (MDRI) for two biomarkers used by the U.S. National HIV Surveillance System for determination of HIV incidence, the Aware BED EIA HIV-1 incidence test (BED) and the avidity-based, modified Bio-Rad HIV-1/HIV-2 plus O ELISA (BRAI) assay. Collectively, 953 specimens from 220 HIV-1 subtype B seroconverters, taken from 5 cohorts, were tested with a biomarker assay. Estimates of MDRI using the non-parametric survival approach were 198.4 days (SD 13.0) for BED and 239.6 days (SD 13.9) for BRAI using cutoff values of 0.8 normalized optical density and 30%, respectively. The probability of remaining in the recent state as a function of time since seroconversion, based upon this revised statistical approach, can be applied in the calculation of annual incidence in the United States.     

Different Profile of mRNA Expression in Sinoatrial Node from Streptozotocin-Induced Diabetic Rat

BackgroundExperiments in isolated perfused heart have shown that heart rate is lower and sinoatrial node (SAN) action potential duration is longer in streptozotocin (STZ)–induced diabetic rat compared to controls. In sino-atrial preparations the pacemaker cycle length and sino-atrial conduction time are prolonged in STZ heart. To further clarify the molecular basis of electrical disturbances in the diabetic heart the profile of mRNA encoding a wide variety of proteins associated with the generation and transmission of electrical activity has been evaluated in the SAN of STZ-induced diabetic rat heart.Conclusions/SignificanceCollectively, this study has demonstrated differences in the profile of mRNA encoding a variety of proteins that are associated with the generation, conduction and regulation of electrical signals in the SAN of STZ-induced diabetic rat heart. Data from this study will provide a basis for a substantial range of future studies to investigate whether these changes in mRNA translate into changes in electrophysiological function.     

Overexpression of LmgshF from Listeria monocytogenes in Indica Rice Confers Salt Stress Tolerance

Russian Journal of Plant Physiology - Glutathione (γ-glutamylcysteinylglycine; GSH), is a multi-functional tri-peptide antioxidant, a key agent in defense against abiotic and biotic stress. A...     

Proteomic comparison of human and great ape blood plasma reveals conserved glycosylation and differences in thyroid hormone metabolism

Most blood plasma proteins are glycosylated. These glycoproteins typically carry sialic acid-bearing sugar chains, which can modify the observed molecular weights and isoelectric points of those proteins during electrophoretic analyses. To explore changes in protein expression and glycosylation that occurred during great ape and human evolution, we subjected multiple blood plasma samples from all these species to high-resolution proteomic analysis. We found very few species-specific differences, indicating a remarkable degree of conservation of plasma protein expression and glycosylation during approximately 12 million years of evolution. A few lineage-specific differences in protein migration were noted among the great apes. The only obvious differences between humans and all great apes were an apparent decrease in transthyretin (prealbumin) and a change in haptoglobin isoforms (the latter was predictable from prior genetic studies). Quantitative studies of transthyretin in samples of blood plasma (synthesized primarily by the liver) and of cerebrospinal fluid (synthesized locally by the choroid plexus of the brain) confirmed approximately 2-fold higher levels in chimpanzees compared to humans. Since transthyretin binds thyroid hormones, we next compared plasma thyroid hormone parameters between humans and chimpanzees. The results indicate significant differences in the status of thyroid hormone metabolism, which represent the first known endocrine difference between these species. Notably, thyroid hormones are known to play major roles in the development, differentiation, and metabolism of many organs and tissues, including the brain and the cranium. Also, transthyretin is known to be the major carrier of thyroid hormone in the cerebrospinal fluid, likely regulating delivery of this hormone to the brain. A potential secondary difference in retinoid (vitamin A) metabolism is also noted. The implications of these findings for explaining unique features of human evolution are discussed.