Lactate from cultures of Lactobacillus casei recovered in a fluidized bed column using ion exchange resin

Summary Lactic acid produced by continuous culture of L.casei in an upflow packed bed reactor, was recovered with Amberlite IRA 400 in a fluidized bed column. Bed expansions of 1.25 and 2.25 were applied. Reutilization did not alter the capability of net recovery of 0.048 ± 0.01 g lactic acid/g resin. When 2200 cm/h of ascensional velocity was used, (bed expansion of 2.25), the resin adsorbed 39.3% of the initial lactic acid and 63.5% was eluted. This resin supported the highest exchange capacity of 0.126 g lactic acid/g resin. Applying high flow rates, the process has potential industrial applications due to the short time employed.     

Intracellular regulation of cell signaling cascades: how location makes a difference

Organelles such as endosomes and the Golgi apparatus play a critical role in regulating signal transmission to the nucleus. Recent experiments have shown that appropriate positioning of these organelles within the intracellular space is critical for effective signal regulation. To understand the mechanism behind this observation, we consider a reaction-diffusion model of an intracellular signaling cascade and investigate the effect on the signaling of intracellular regulation in the form of a small release of phosphorylated signaling protein, kinase, and/or phosphatase. Variational analysis is applied to characterize the most effective regions for the localization of this intracellular regulation. The results demonstrate that signals reaching the nucleus are most effectively regulated by localizing the release of phosphorylated substrate protein and kinase near the nucleus. Phosphatase release, on the other hand, is nearly equally effective throughout the intracellular space. The effectiveness of the intracellular regulation is affected strongly by the characteristics of signal propagation through the cascade. For signals that are amplified as they propagate through the cascade, reactions in the upstream levels of the cascade exhibit much larger sensitivities to regulation by release of phosphorylated substrate protein and kinase than downstream reactions. On the other hand, for signals that decay through the cascade, downstream reactions exhibit larger sensitivity than upstream reactions. For regulation by phosphatase release, all reactions within the cascade show large sensitivity for amplified signals but lose this sensitivity for decaying signals. We use the analysis to develop a simple model of endosome-mediated regulation of cell signaling. The results demonstrate that signal regulation by the modeled endosome is most effective when the endosome is positioned in the vicinity of the nucleus. The present findings may explain at least in part why endosomes in many cell types localize near the nucleus.     

The parameters of cardiac-muscle repolarization: The measurement and information value

We performed a comparative analysis of different classes of algorithms for computer-assisted cardiological diagnostics. The concepts of an “internal” and “external” image of myocardial ischemia were formulated. We also discussed the biophysical aspects for the basic indices of spatial heterogeneity of the repolarization process in the myocardium, as well as the problems of measurement of the corresponding parameters. The experimental part was performed on two groups of patients. Both experimental and control groups included two sets of 12-lead electrocardiograms of real patients: “Normal” and “Ischemia” (with lateral localization). The experimental group consisted of 202 and 143 electrocardiograms, while the control group consisted of 200 and 91 electrocardiograms, respectively. The electrocardiograms were verified according to the Minnesota Code criteria.     

Protective effects of manganese, cobalt, nickel, and barium against a calcium paradox in the isolated frog heart

The effect of inorganic slow channel blockers on the calcium paradox in the frog heart was examined. Addition of the divalent cations of manganese, cobalt, nickel, or barium during calcium depletion protected the frog heart against a calcium paradox. This protective effect was indicated by reduced protein release, maintenance of electrical activity, and recovery of mechanical activity during reperfusion. Tissue calcium determination results showed that in the control paradox in the absence of divalent cations, there is an efflux of calcium from myocardial cells during calcium depletion and a massive influx of calcium during the following reperfusion, leading to a calcium overload. Divalent cations protected frog myocardial cells, when present in the calcium-free perfusion medium, by reducing both calcium efflux during calcium depletion and the massive calcium influx during reperfusion. The effectiveness of the added divalent cations showed a strong dependence upon their ionic radius. The most potent inhibitors of the calcium paradox in the frog heart were the divalent cations having an ionic radius closer to the ionic radius of calcium. These results are discussed in terms of the possible mechanism involved in the protective effect of manganese, cobalt, nickel, and barium.     

A simple model describing the kinetics of the xanthophyll cycle.

A new kinetic model of the xanthophyll cycle is proposed. The model is based on the assumption that the light-dependent interconversion of the so-called available and unavailable violaxanthin constitutes the rate-limiting process of the cycle at intermediate, non-saturating light intensities. This assumption, together with the known properties of violaxanthin de-epoxidase, explains all specific features of the experimental facts.     

Stress-induced rearrangement of Fusarium retrotransposon sequences

Rearrangement of Fusarium oxysporum retro- transposon skippy was induced by growth in the presence of potassium chlorate. Three fungal strains, one sensitive to chlorate (Co60) and two resistant to chlorate and deficient for nitrate reductase (Co65 and Co94), were studied by Southern analysis of their genomic DNA. Polymorphism was detected in their hybridization banding pattern, relative to the wild type grown in the absence of chlorate, using various enzymes with or without restriction sites within the retrotransposon. Results were consistent with the assumption that three different events had occurred in strain Co60: genomic amplification of skippy yielding tandem arrays of the element, generation of new skippy sequences, and deletion of skippy sequences. Amplification of Co60 genomic DNA using the polymerase chain reaction and divergent primers derived from the retrotransposon generated a new band, corresponding to one long terminal repeat plus flanking sequences, that was not present in the wild-type strain. Molecular analysis of nitrate reductase-deficient mutants showed that generation and deletion of skippy sequences, but not genomic amplification in tandem repeats, had occurred in their genomes.