Hydrodynamic studies of a Annular Circulating Fluidised Bed Drier with sand particles

The hydrodynamics of Annular Circulating Fluidised Bed Drier (ACFBD) has been studied with sand particles of diameter 928?m and density 2650?kg/m³. The gap opening was varied from 12 to 48?mm and the mass flux of solids was found to be constant for the gap openings greater than 44?mm. Two regimes, slugging dense flow and dilute phase flow were identified and models were proposed for pressure drop calculation for the two regimes. An erratic factor has been introduced for the slugging dense flow regime. The models agreed with the experimental data with an error of less than 20%.     

Nitrogen Fixation and Carbon Dioxide Assimilation in Rhizobium japonicum

In free-living Rhizobium japonicum cultures, the stimulatory effect of CO₂ on nitrogenase (acetylene reduction) activity was mediated through ribulose bisphosphate carboxylase activity. Two mutant strains (CJ5 and CJ6) of R. japonicum defective in CO₂ fixation were isolated by mitomycin C treatment. No ribulose bisphosphate carboxylase activity could be detected in strain CJ6, but a low level of enzyme activity was present in strain CJ5. Mutant strain CJ5 also exhibited pleiotropic effects on carbon metabolism. The mutant strains possessed reduced levels of hydrogen uptake, formate dehydrogenase, and phosphoribulokinase activities, which indicated a regulatory relationship between these enzymes. The CO₂-dependent stimulation of nitrogenase activity was not observed in the mutant strains. Both mutant strains nodulated soybean plants and fixed nitrogen at rates comparable to that of the wild-type strain.     

Malate dehydrogenases from actinomycetes: structural comparison of Thermoactinomyces enzyme with other actinomycete and Bacillus enzymes.

Malate dehydrogenases from bacteria belonging to the genus Thermoactinomyces are tetrameric, like those from Bacillus spp., and exhibit a high degree of structural homology to Bacillus malate dehydrogenase as judged by immunological cross-reactivity. Malate dehydrogenases from other actinomycetes are dimers and do not cross-react with antibodies to Bacillus malate dehydrogenase.     

Molecular structure by the constrained damped least-squares (CDLS) method

A method for simulating three-dimensional molecular structure is presented. The method can satisfy any number of constraints on the molecular structure. The constraints can pertain to the constancy of individual distances and angles or be related to point-group symmetry. A simulated three-dimonsional model is forced to satisfy the required constraints in the least-squares sense. The least-squares optimization is damped to guard against convergence failure. This method is suggested as a tool to obtain approximate molecular structure in situations where a number of quantitative features are known about a molecular structure from preliminary crystallographic results but not the full molecular structure. An application to the structure of enniatin B–K⁺ complex is given to illustrate such a use.     

A facile method for the isolation of porcine heart mitochondrial malate dehydrogenase by affinity elution chromatography on Procion Red HE3B

A quick, simple method has been devised for isolating pig heart mitochondrial malate dehydrogenase in apparently homogeneous state and good yield. It entails the adsorption of the enzyme to agarose-linked Procion Red HE3B and specific elution of a ternary complex consisting of the malate dehydrogenase, NAD+, and L-malate.     

Flow rate dependent kinetics of urease immobilized onto diverse matrices

Gas holdup and liquid circulation velocity meassurements were made for a range of liquid viscosities in a 22 l external loop airlift column and 250 l pilot-scale concentric cylinder airlift bioreactor. The results showed that for a fixed superficial gas velocity, liquid circulation velocity decreased monotonically with increasing liquid viscosity. The gas holdup for a fixed gas flow rate showed an initial increase with liquid viscosity followed by a decrease when liquid viscosity increased beyond a critical value. These observations could not be described satisfactorily using the available models of gas holdup and liquid circulation.List of Symbols U _sg m/s Superficial gas velocity - U _sl m/s Superficial liquid velocity in the riser Greek Letters Pas Liquid viscosity - _g Gas holdup in the riser     

Ras is required for a limited number of cell fates and not for general proliferation in Caenorhabditis elegans.

Experiments with mammalian tissue culture cells have implicated the small GTPase Ras in the control of cellular proliferation. Evidence is presented here that this is not the case for a living animal, the nematode Caenorhabditis elegans: proliferation late in embryogenesis and throughout the four larval stages is not noticeably affected in animals lacking Ras in various parts of their cell lineages. Instead, genetic mosaic analysis of the let-60 gene suggests that Ras is required only, at least later in development (a maternal effect cannot be excluded), for establishment of a few temporally and spatially distinct cell fates. Only one of these, the duct cell fate, appears to be essential for viability.     

Isocitrate Lyase from a Thermophilic Bacillus: Effect of Salts on Enzyme Activity

The isocitrate lyase from a thermophilic Bacillus is activated about threefold by a variety of salts. Such strong stimulation of activity is not seen with isocitrate lyase from the mesophiles, Bacillus licheniformis, Bacillus megaterium, Escherichia coli, and Aspergillus nidulans. The salt activation is markedly pH-dependent. At pH values above 8.6, salt (KCl) indeed inhibits the enzyme activity. Potassium chloride also causes a significant shift of the pH optimum of the enzyme towards the acid side. As the temperature of the enzyme reaction is raised, activation becomes progressively weaker. Potassium chloride also affords considerable protection against enzyme denaturation at 55 C. The activation and the stabilization, however, appear to be independent effects. Of six other enzymes in the thermophile that were examined, isocitrate dehydrogenase was equally strongly activated by KCl and malate synthase was less strongly, but significantly, activated; citrate synthase, malate dehydrogenase, glutamate dehydrogenase, and lactate dehydrogenase were unaffected or slightly inhibited by KCl. The property of being strongly activated by salt appears to be a peculiar characteristic of the thermophile isocitrate lyase and possibly evolved concomitantly with its thermostability.     

Physiological Role of Pyruvate Carboxylase in a Thermophilic Bacillus

A prototrophic, thermophilic bacillus is in a state of biotin insufficiency when grown in medium consisting of inorganic salts and a carbon source. The effect of this biotin deficiency on the growth rate is severe only if the functioning of pyruvate carboxylase is essential for the utilization of the particular growth substrate. A mutant, PC2, of the thermophile devoid of active pyruvate carboxylase has been isolated. The properties of this mutant confirm the anaplerotic role of this enzyme in the utilization for growth of compounds like glucose and lactate which are catabolized via pyruvate. This conclusion is supported by the finding that revertants isolated from strain PC2 have regained simultaneously the ability to synthesize active pyruvate carboxylase and the ability to utilize glucose or lactate for growth. The growth of mutant PC2 on acetate, unlike that of the parent wild type, is inhibited when glucose or lactate is added to the medium. Secondary mutants obtained from PC2, which are resistant to such inhibition, still carry the original pyruvate carboxylase lesion but are derepressed for isocitrate lyase. This suggests that the inhibition of the growth of mutant PC2 is due to a block in the functioning of the glyoxylate cycle, produced by the glucose or lactate supplement.