1,721,068 research outputs found
Biochemical evidence for multiple acetoin-forming enzymes in cultured plant cells
No full textAcetoin (3-hydroxy-2-butanon) production was investigated in extracts from suspension cultured cells of carrot, tobacco, maize and rice. Crude extracts were able to catalyze acetoin synthesis from pyruvate and/or acetaldehyde at rates ranging from 0.02 to 0.1 mkat kg-1 protein, while no evidence was found for acetolactate-deriving acetoin production. Three acetoin-forming enzymes were resolved upon adsorption chromatography. A minor peak of activity was deduced as due to a partial, non-enzymatic decarboxylation of the acetolactate produced by acetolactate synthase under the same experimental conditions, being completely abolished by the addition of an acetolactate synthase inhibitor. The other two activities were characterized following further purification by gel filtration chromatography. A low molar ratio between acetoin production and pyruvate utilization, the capability of producing acetaldehyde from pyruvate at higher rate, an optimal activity at acidic pH values and its increase in extracts from cells grown under hypoxic condition strongly suggested the former as a side reaction of pyruvate decarboxylase. The latter activity, which showed maximal rate at neutral pH values, was on the contrary found to quantitatively convert acetaldehyde and pyruvate to acetoin. This pyruvate carboligase, which increased in actively proliferating cells and declined in a late logarithmic phase and was not induced under anaerobiosis, was present at similar levels in all four plant species
Biochemical evidence for multiple acetoin-forming enzymes in cultured plant cells
No full textAcetoin (3-hydroxy-2-butanon) production was investigated in extracts from suspension cultured cells of carrot, tobacco, maize and rice. Crude extracts were able to catalyze acetoin synthesis from pyruvate and/or acetaldehyde at rates ranging from 0.02 to 0.1 mkat kg(-1) protein, while no evidence was found for acetolactate-deriving acetoin production. Three acetoin-forming enzymes were resolved upon adsorption chromatography. A minor peak of activity was deduced as due to a partial, nonenzymatic decarboxylation of the acetolactate produced by acetolactate synthase under the same experimental conditions, being completely abolished by the addition of an acetolactate synthase inhibitor. The other two activities were characterized following further purification by gel filtration chromatography. A low molar ratio between acetoin production and pyruvate utilization, the capability of producing acetaldehyde from pyruvate at higher rate, an optimal activity at acidic pH values and its increase in extracts from cells grown under hypoxic condition strongly suggested the former as a side reaction of pyruvate decarboxylase. The latter activity, which showed maximal rate at neutral pH values, was on the contrary found to quantitatively convert acetaldehyde and pyruvate to acetoin. This pyruvate carboligase, which increased in actively proliferating cells and declined in a late logarithmic phase and was not induced under anaerobiosis, was present at similar levels in all four plant species
The Effect of DLVO, hydrophilic and hydrophobic energies on the aggregation of cells in solution
No full textDifferential sensitivity of plant-associated bacteria to sulfonylurea and imidazolinone herbicides
No full textThe side effects of sulfonylurea and imidazolinone herbicides on plant-associated bacteria were investigated under pure culture conditions. Eighteen isolates, belonging to the genera Azotobacter Azospirillum, Bacillus, Enterobacter Pseudomonas and Serratia, were exposed to four active compounds at concentration ranges similar to those in field soil. The sulfonylureas chlorsulfuron and rimsulfuron inhibited the growth of one of two Azospirillum and one of four Pseudomonas strains, while the imidazolinones imazapyr and imazethapyr were effective on two out of five Bacillus isolates. Surfactants in commercial formulation significantly enhanced rimsulfuron toxicity. With the exception of one Azospirillum strain, the differential tolerance of rhizobacteria to these herbicides was related to a differential sensitivity of their target, the activity of the first enzyme in branched-chain amino acid biosynthesis, acetohydroxyacid synthase (AHAS)
Protein-surface interactions: an energy based mathematical model
No full textThis article describes an energy-based approach to protein adsorption, focusing on the energies involved in the interactions between a protein and a surface. Mathematical modeling and simulation based on this approach allow an improved understanding of the conditions that favor or prevent adsorption of a protein onto a surface and that can play a significant role in the design of material surfaces that interact with biological tissues according to specific needs. Biocompatibility with respect to fluids in motion, such as blood, is the main foreseeable application of our work. The considered energies are the van der Waals energy, the electrostatic energy, and the hydrophobic or hydrophilic energy. Moreover, the motion of the medium in which particles are immersed is also taken into account, considering the drag effect of the motion of the fluid on the particle, leading to a kinetic contribution to the total energy. It is shown that the adsorption behavior is not mainly determined by the van der Waals energy and by the double layer energy, but that a significant role is also played by the hydrophobic or hydrophilic energy. These results support the findings of experimental studies
Electroviscosity: a mathematical model and its relationship with the adhesion behaviour of particles at a surface
No full text
A computer model of the influence of electroviscosity on the kinetic energy of a particle flowing in a vessel
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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