Protein precipitate recovery using microporous membranes

The use of microporous membranes has been examined for the recovery of precipitated protein suspensions and related soluble protein. Membrane flux rates and soluble protein transmissions are reported for unstirred batch-cell studies and cross-flow experiments. The unstirred batch-cell gave soluble protein transmissions in the range 80-100% for feeds containing either soluble protein or a mix of soluble and isoelectrically precipitated protein. In all cases a sharp decline in flux was observed which was, for example, considerably greater for soluble protein at its isoelectric point, pH 4.6, than at pH 8.8. The presence of precipitated protein led to a further decrease in flux rate. In cross-flow studies, flux decline was eventually accompanied by a significant decline in soluble protein transmission. The flux protein-transmission characteristics of microporous membranes are discussed in terms of the interaction of the soluble and precipitated protein with the membrane.     

On-line adaptive control of a fed-batch fermentation of Saccharomyces cerevisiae

The feasibility of applying an adaptive control technique to a fermentation process is investigated. The nonlinear, time-variant parameters of a fermentation process were estimated on-line as a series of linearized describing matrices. The matrices were used to update a suboptimal feedback law which controlled the process in real time over the linear region. Experiments were performed on a small-scale fully instrumented fermenter with the online, real-time adaptive control package. Results are presented for both single- and multivariable control, and indicate successful control of yeast cell growth.     

Regeneration of NAD(+) cofactor by photosensitized electron transfer in an immobilized alcohol dehydrogenase system

The irradiation with visible light of a photosensitizer dye like methylene blue was used to regenerate by electron transfer the oxidized form of a pyridine nucleotide coenzyme (NAD(+)). The process has been studied on a common enzymatic reaction: ethanol oxidation by alcohol-NAD(+) oxidoreductase immobilized on polyacrylamide gel or porous glass balls. In the experimental conditions used, the initial NAD(+) recycling rates were 2.33 x 10(4) cycles/h (polyacrylamide) and 3 x 10(4) cycles/h (glass balls). A total number of 49.5 x 10(4) cycles was obtained for 13 runs of 2 h. The enzyme immobilization strongly increased its stability: after 28 days at 20 degrees C, the residual activity was 25% of the initial value.     

Methane recovery from water hyacinth through anaerobic activated sludge process

The concepts of phase separation, anaerobic activated sludge process, and alkali pretreatment have been incorporated in this investigation with the objective of developing rational and cost-effective designs of diphasic anaerobic activated sludge systems, with and without alkali treatment, for methane recovery from water hyacinth (WH). Evaluation of process kinetics and optimization analyses of laboratory data reveal that a diphasic system with alkali treatment could be designed with an alkali pretreatment step (3.6% Na(2)CO(3) + 2.5% Ca(OH)(2) (w/w) of WH, 24 h duration) followed by an open acid phase (2.1 days HRT) and closed methane reactor with sludge recycle (5.7 days HRT, 7.7 days MCRT) for gas yield of 50 L/kg WH/d at 35-37 degrees C. Likewise, a diphasic system without alkali treatment could be designed with an open acid phase (2 days HRT) followed by closed methane reactor with sludge recycle (3.2 days HRT, 6 days MCRT) for gas yield of 32.5 L/kg WH/d at 35-37 degrees C. Detailed economic analyses bring forth greater cost-efficacy of the diphasic system without alkali treatment and reveal that the advantage accrued in terms of higher gas yield is overshadowed by the cost of chemicals in the diphasic system with alkali treatment.     

Coimmobilization of substrate and biocatalyst: A method for bioconversion of poorly soluble substances in water milieu

Coimmobilization of biocatalyst and substrate was studied as a method to increase the conversion rate in systems with substrates of extremely low solubility in water. The system studied was the conversion of hydrocortisone to prednisolone by Arthrobacter simplex. As a matrix for coimmobilization, alginate turned out to be superior to agar and agarose. After the reaction was complete, the beads were solubilized, andthe cells recovered for reuse, by centrifugation, whereas the prednisolone was extracted from the supernatant.     

Kinetic characterization of reduced pyridine nucleotide dehydrogenases (duroquinone-dependent) in cucurbita microsomes

Stomatal conductances of normally oriented and inverted leaves were measured as light levels (photosynthetic photon flux densities) were increased to determine whether abaxial stomata of Vicia faba leaves were more sensitive to light than adaxial stomata. Light levels were increased over uniform populations of leaves of plants grown in an environmental chamber. Adaxial stomata of inverted leaves reached maximum water vapor conductances at a light level of 60 micromoles per square meter per second, the same light level at which abaxial stomata of normally oriented leaves reached maximum conductances. Abaxial stomata of inverted leaves reached maximum conductances at a light level of 500 micromoles per square meter per second, the same light level at which adaxial stomata of normally oriented leaves reached maximum conductances. Maximum conductances in both normally oriented and inverted leaves were about 200 millimoles per square meter per second for adaxial stomata and 330 millimoles per square meter per second for abaxial stomata. Regardless of whether leaves were normally oriented or inverted, when light levels were increased to values high enough that upper leaf surfaces reached maximum conductances (about 500 micromoles per square meter per second), light levels incident on lower, shaded leaf surfaces were just sufficient (about 60 micromoles per square meter per second) for stomata of those surfaces to reach maximum conductances. This `coordinated' stomatal opening on the separate epidermes resulted in total leaf conductances for normally oriented and inverted leaves that were the same at any given light level. We conclude that stomata in abaxial epidermes of intact Vicia leaves are not more sensitive to light than those in adaxial epidermes, and that stomata in leaves of this plant do not respond to light alone. Additional factors in bulk leaf tissue probably produce coordinated stomatal opening on upper and lower leaf epidermes to optimally meet photosynthetic requirements of the whole leaf for CO₂.     

Regulation of Gene Expression in Developing Zea mays Embryos: Protein Synthesis during Embryogenesis and Early Germination of Maize

Polypeptides synthesized in dissected embryos of Zea mays at different stages of embryogenesis and early germination have been characterized by their migration in two-dimensional gel electrophoresis. This analysis has been carried out with in vivo labeled polypeptides from excised embryos and with proteins synthesized in vitro in the rabbit reticulocyte system directed by poly(A⁺) RNA isolated from the different developmental stages. We have identified three main sets of expressed polypeptides: (a) embryonic set: this group of polypeptides is synthesized in young and mature embryos but not in early germination; (b) maturation set: this group of polypeptides is not present in young embryos and appears during the maturation period. Some of these polypeptides are still present in early germination while others disappear from stored mRNAs in dry embryos. One particular group from this set can be induced prematurely in young embryos by incubation with abscisic acid; and (c) germination set: this group of polypeptides is not expressed in the maturation period and appears after brief imbibition of the dry embryos.     

Essentiality of Boron for Dinitrogen Fixation in Anabaena sp. PCC 7119

The relationship between the requirement for boron and the form of N supplied in nutrient media to cyanobacterium Anabaena sp. PCC 7119 was investigated. When cells were grown in a medium which contained nitrate or ammonium-N, boron deficiency in the nutrient media did not inhibit growth or change cell composition. However, when cells were dependent on N₂ fixation, the lack of boron inhibited growth (i.e. growth ceased after 96 hours under these conditions). Additionally, boron-deficient cells showed a significant decrease in their content of phycobiliproteins and chlorophyll and accumulated carbohydrates within 24 hours of removing boron from the nutrient media. Inhibition of photosynthetic O₂ evolution accompanied the decrease in photosynthetic pigments. Boron deficiency symptoms were relieved when either boron or combined N was added to boron-deficient cultures. The degree of recovery depended upon the age of the cultures. Assays of nitrogenase activity showed that, after 2 hours of growth, nitrogenase activity of boron-deficient cells was inhibited by 40%. After 24 hours a total inactivation of nitrogenase activity was observed in boron-deficient cells. These results strongly suggest an involvement of boron in N₂ fixation in cyanobacteria.     

Effect of Monochromatic Light on Proton Efflux of the Blue-Green Alga Anabaena variabilis

Light-induced proton efflux of Anabaena variabilis was found to be biphasic, the second phase being inhibited by the ATPase inhibitor nitrofen (2,4-dichloro-1-[4-nitrophenoxy]benzene). The first, fast phase was triggered by monochromatic light of 707 nanometers, whereas the second, slower phase was not. With 707 nanometers, light, respiratory O₂ uptake was inhibited. Using light composed of two wavelengths (616 and 707 nanometers) a marked enhancement of both O₂ evolution as well as the second phase of proton efflux was observed. The first phase was not enhanced. Thus, phase II is driven by both photosystems. As concluded from the action spectrum phase I is markedly determined by photosystem-I activity. Altogether the data show that two different mechanisms of light-induced proton efflux exist on the cytoplasmic membrane of Anabaena, the slower one being dependent on ATP and linear photosynthetic electron flow.