Glycoprotein Synthesis in Plants: II. Structure of the Mannolipid Intermediate

This paper reports the purification and structural determination of the mannolipid shown previously (Ericson and Delmer 1977 Plant Physiol 59: 341-347) to serve as an intermediate in glycoprotein synthesis in cotyledons of Phaseolus vulgaris. The mannolipid was purified by chromatography in organic solvents on diethylaminoethyl-cellulose, followed by repeated steps of deacylation and rechromatography on Sephadex LH-20. Binding and elution behavior on diethylaminoethyl-cellulose was consistent with the presence of a monophosphate residue. Lability of the mannolipid to mild acid treatment as well as its resistance to hot phenol treatment or catalytic hydrogenation are consistent with the structure of a polyprenol having a saturated α-residue. After methanolysis, the chloroform-methanol-soluble portion of the mannolipid was analyzed by mass spectrometry. The fragmentation pattern obtained was nearly identical to that obtained from standard dolichol-phosphate. An intense ion at m/e 69 represented the ω-terminal isoprenoid residue, and repeating fragments separated by 68 mass units were observed up to m/e of > 1,200. All evidence supports the conclusion that the mannolipid is dolichol-monophosphate-mannose and thus provides further support for the concept that the processes involved in the glycosylation of protein in higher plants are similar to those known to occur in the animal kingdom.     

Distribution and behavior of sludge in upflow reactors for anaerobic treatment of wastewater

A model has been developed and experimentally checked for the physical behavior of sludge in the blanket in upflow reactors. The model is based on the mass balance for the sludge in the blanket, and can be used to predict the distribution of sludge in an upflow reactor in relation with the gas production, sludge settling characteristics, and the linear fluid velocity in the reactor. The quantitative values of the transport factors that are a measure of the efficiency of the transport of sludge by the fluid streams occurring in the reactor were determined experimentally in reactors of 30- and 200-m(3) volumes. As this was done for wastewater containing lower fatty acids as the main organic pollutants and for sludge with good settling characteristics, the predictive value of the model is limited. It may be used for the second (methane forming) step of anaerobic treatment of wastewater.     

Dynamic simulator for anaerobic digestion processes

A transient, two-culture model simulating methane production from biomass has been developed. The simulator, based partially on the work by Andrews and McCarty, is capable of calculating the hydrolysis products of several common organic materials, accommodating various substrate feeding modes, and simulating the transient physico-biochemical transport and conversion processes occurring in the biological, liquid, and gaseous phases of a well-mixed reactor. The mathematical representation of this bioconversion system consists of a set of 11 coupled, nonlinear first-order rate equations based on the principles of mass conservation and biochemical reaction kinetics. The model can be used in conjunction with laboratory investigations and as a simulator for evaluating process control strategies and cost developments.     

Relative contributions of biological and chemical reactions to the overall rate of pyrite oxidation at temperatures between 30 degrees C and 70 degrees C

The stoichiometry and kinetics of the spontaneous, chemical reaction between pyrite and ferric iron was studied at 30, 45, and 70 degrees C in shake flasks at pH 1.5 by monitoring the ferrous iron, total iron, elemental sulfur, and sulfate concentration profiles in time. It was found that the sulfur moiety of pyrite was oxidized completely to sulfate. Elemental sulfur was not produced in detectable amounts. The iron moiety of pyrite was released as ferrous iron. All observed initial reaction rates could be fitted into an empirical equation. This equation includes the concentrations of ferric iron and pyrite, and a constant which is dependent on the temperature and the nature of the main anion present. It was observed that ferrous iron formed during the reaction slowed down the oxidation of pyrite by ferric iron. The extent of this effect decreased with increasing temperature. With the aid of the empirical equation, the contribution of the chemical oxidation of pyrite by ferric iron to the overall oxidation in a hypothetical plug-flow reactor, in which biologically mediated oxdidation of pyrite and ferrous iron by oxygen also takes place, can be assessed. At 30, 45, and 70 degrees C, respectively, 2, 8-17, and 43% of the pyrite was oxidized chemically by ferric iron. Therefore, it is expected that only in reactors operating at high temperatures with extremely thermophilic bacteria, will chemical oxidation cause a significant deviation from the apparent first order overall kinetics of biological pyrite oxidation.     

Influence of mass transfer limitations on determination of the half saturation constant for hydrogen uptake in a mixed-culture CH(4)-producing enrichment

There is strong evidence in the literature supporting the existence of significant mass transfer limitations on the kinetics of exogenous H(2) consumption by methanogens. The half saturation constant for H (2) uptake by a mixed-culture, CH(4) producing enrichment was measured using an experimental protocol that avoided internal mass transfer limitations. The value obtained was two orders of magnitude smaller than any other previously reported. A mathematical model for acetogenic syntrophic associations was developed to check the capacity of H(2) as electron transporter between syntrophic partners. It was found that H(2) diffusion could account for the rate of transport of electrons between the syntrophic microorganisms and that formate is not a necessary intermediate. The possibility that formate may be an intermediate in this system was not ruled out. A Monod-type kinetic equation was modified to include the observed H(2) threshold effect. This modified equation was used to predict the CH(4)-production rate in a batch-fed digester. The results show that the external and internal H(2) pools are kinetically coupled. (c) 1992 John Wiley & Sons, Inc.     

A two-step enzymatic synthesis of dipeptides

A simple system is introduced to produce dipeptides continuously by enzyme catalyzed condensation of amino acid esters and amino acid amides. Synthesis of N-terminal free dipeptide-amides is achieved by means of carboxypeptidase Y. The peptide-amide is deamidated utilizing a newly isolated peptide-amide is deamidated utilizing a newly isolated peptide-amidase. Separation of substrates and products is accomplished by anion-exchange chromatography. Modeling of the reactions shows that the two reactions have to be carried out in a cascade of two reactors in order to prevent hydrolysis of the peptide by the carboxypeptidase. Continuous production of Kyotorphin (H-TyrArg-OH) with a space-time yield of 257 g/L . d shows the feasibility of this concept.     

Mechanism of enhanced oxygen transfer in fermentation using emulsified oxygen-vectors

Limitations of oxygen transfer in fermentation can be solved using auxiliary liquids immiscible in the aqueous phase. The liquids (called oxygen-vectors) used in this study were hydrocarbon (n-dodecane) and perfluorocarbon (forane F66E) in which oxygen is highly soluble (54.9 mg/L in n-dodecane and 118 mg/L in forane F66E at 35 degrees C in contact with air at atmospheric pressure). It has been demonstrated that the use of n-dodecane emulsion in a culture of Aerobacter aerogenes enabled a 3. 5-fold increase of the volumetric oxygen transfer coefficient(k(L)a) calculated on a per-liter aqueous phase basis. The droplet size of the vector played a crucial role in the phenomena. When a static contact between gas bubble and vector droplet was established in water, the vector covered the bubble, in agreement with positive values of the spreading coefficient for these fluids. The determination of the oxygen transfer coefficients (k(L)) in a reactor with a definite interfacial area enabled the main resistance to be located in the boundary layer of the waterside either for a gas-water or a vector-water interface. Because oxygen consumption by weakly hydrophobic cells can only occur in the aqueous phase, the oxygen transfer is achieved according to the following pathway: gas-vector-water-cell. Finally, a mechanism for oxygen transfer within this four-phased system is proposed.