Effects of glucose and phenol on soluble microbial products (SMP) in sequencing batch reactor systems

Soluble microbial products (SMP) are ubiquitously present in the effluents of biological wastewater treatment systems. In sequencing batch reactor (SBR) systems, effects of influent concentration and temperature on the amount and the molecular weight (MW) distribution of SMP were investigated for the two substrates, glucose and phenol. The values of effluent SMP/S₀ of phenol were higher than those of glucose at different influent concentrations and temperatures. It was found that the effluent SMP (S_e) was linearly correlated to the influent total organic carbon (TOC) (S₀) for both substrates. The slope and intercept of the equation were affected by the temperature. According to the analysis of the MW distribution, it was shown that there exists a bimodal pattern with the majority of SMP having a MW<1 kDa or >10 kDa. The low MW fraction (<1 kDa) amounts to 47.3–70.4% of the effluent SMP. The high MW fraction (>10 kDa) slightly fluctuates in the range of 21.2–32.8% of the effluent SMP.     

Alkaline hydrothermal conversion of cellulose to bio-oil: influence of alkalinity on reaction pathway change

The effects of alkalinity on alkaline hydrothermal conversion (alkaline-HTC) of cellulose to bio-oil were investigated in this study. The results showed that the initial alkalinity greatly influenced the reaction pathways. Under initial strong alkaline conditions with final pH greater than 7, alkaline-HTC only followed the alkaline pathway. However, under initial weak alkaline conditions with final pH of less than 7, acidic as well as alkaline pathways were involved. The main mechanism behind this change of reaction pathways under weak alkaline conditions was that carboxylic acids were first formed from cellulose via the alkaline pathway and then neutralized/acidified the alkaline solutions. Once the pH of the alkaline solutions decreased to less than 7, the acidic instead of the alkaline reaction pathway occurred. This change of the reaction pathways with initial alkalinity partly explained the inconsistent results in the literature of alkaline-HTC bio-oil compositions and yields.     

Kinetic characterisation of enzymatic esterification in a solvent system: adsorptive control of water with molecular sieves

The kinetics of enzymatic esterification of glycerol with oleic acid, in equimolar ratio, catalyzed by immobilized Mucor miehei lipase in a solvent system in the presence of the molecular sieves was carried out at 37°C at different Lipozym and solvent (n-hexane) concentrations and the molecular sieve contents were studied in a batch stirred-tank reactor (BSTR). The reactions were followed by the determination of reaction conversions during 45 h. The experimental data of enzymatic esterification of glycerol with oleic acid in a solvent system in the presence of molecular sieves showed minimal deviation from the calculated value in the irreversible second order kinetic model. On the basis of the experimental data, we found an empirical correlation between concentrations of Lipozym, concentrations of solvent (n-hexane), contents of the molecular sieve and the reaction rate constant, k₁.     

Characterization of human nicotinate phosphoribosyltransferase: Kinetic studies, structure prediction and functional analysis by site-directed mutagenesis

Nicotinate phosphoribosyltransferase (NaPRT, EC 2.4.2.11) catalyzes the conversion of nicotinate (Na) to nicotinate mononucleotide, the first reaction of the Preiss-Handler pathway for the biosynthesis of NAD(+). Even though NaPRT activity has been described to be responsible for the ability of Na to increase NAD(+) levels in human cells more effectively than nicotinamide (Nam), so far a limited number of studies on the human NaPRT have appeared. Here, extensive characterization of a recombinant human NaPRT is reported. We determined its major kinetic parameters and assayed the influence of different compounds on its enzymatic activity. In particular, ATP showed an apparent dual stimulation/inhibition effect at low/high substrates saturation, respectively, consistent with a negative cooperativity model, whereas inorganic phosphate was found to act as an activator. Among other metabolites assayed, including nucleotides, nucleosides, and intermediates of carbohydrates metabolism, some showed inhibitory properties, i.e. CoA, several acyl-CoAs, glyceraldehyde 3-phosphate, phosphoenolpyruvate, and fructose 1,6-bisphosphate, whereas dihydroxyacetone phosphate and pyruvate exerted a stimulatory effect. Furthermore, in light of the absence of crystallographic data, we performed homology modeling to predict the protein three-dimensional structure, and molecular docking simulations to identify residues involved in the recognition and stabilization of several ligands. Most of these residues resulted universally conserved among NaPRTs, and, in this study, their importance for enzyme activity was validated through site-directed mutagenesis.     

Molecular Characterization of GP50: A Neuron-Specific, Synaptic-Enriched Glycoprotein

The molecular properties of the neuron-specific, synaptic-enriched glycoprotein GP50 have been investigated with the aid of the monoclonal antibody MabSM-GP50. GP50 immunoreactivity was detected in the brains of the frog, trout, pigeon, snake, rabbit, mouse, cow, and human, although variation in quantity and electrophoretic mobility of the immunoreactive protein between species was apparent. Deglycosylation of synaptic membranes (SMs) with endoglycosidase H, peptide:N-glycosidase F, trifluoromethane-sulfonic acid, and alkaline sodium borohydride indicated that GP50 is associated primarily, if not exclusively, with high-mannose and/or hybrid-type oligosaccharides and lacks complex N-linked and O-linked sugar chains. GP50 remained associated with the membrane fraction following extraction of SMs with alkaline sodium carbonate, was partially (55%) present in the detergent phase following the phase partitioning of SMs in the presence of Triton X-114, and was resistant to proteolytic digestion with trypsin when present as a component of intact membranes. Taken together, these results indicate that GP50 is an integral component of the SM. Sucrose gradient centrifugation of Triton X-100 extracts of SMs or of forebrain and cerebellar homogenates resolved GP50 into two fractions with sedimentation coefficients of 3.6S and 7.3S, which accounted for 45 and 55% of the total, respectively. The 7.3S form occurred exclusively in the aqueous phase following partitioning with Triton X-114, whereas the 3.6S species was found in both the aqueous and detergent phases.(ABSTRACT TRUNCATED AT 250 WORDS)