Bioelectrochemistry and bioenergetics (Lausanne, Switzerland)最新文献

This work presents the results of a study, carried out by recently developed amperometric bioelectrodes, on the interactions between carbonic anhydrase (CA) and the decarboxylating enzymes arginine decarboxylase (ADC), l-lysine decarboxylase (LDC), and l-ornithine decarboxylase (ODC). These are all pyridoxal-phosphate dependent enzymes and catalyze the decarboxylation reaction of the respective amino acids, to give carbon dioxide and the corresponding diamine (agmatine, cadaverine, and putrescine, respectively). The rate of each decarboxylase catalyzed reaction was measured by monitoring the production of the respective diamine by a plant tissue diamino oxidase (DAO) based bioelectrode. DAO is the enzyme which catalyzes the oxidation of agmatine, cadaverine, and putrescine with the production of NH₃ and H₂O₂. DAO-based bioelectrodes consist of an amperometric H₂O₂ electrode, coupled to the biocatalytic membrane formed by a whole plant tissue (lentil cotyledon) containing the enzyme DAO, immobilized on a dialysis membrane by polyazetidine prepolymer (PAP). The bioelectrodes were calibrated and characterized in standard solutions of agmatine, cadaverine, and putrescine. Kinetic studies to measure decarboxylase activity were performed in the presence of different concentrations of ADC, LDC, and ODC, resulting in a lowest detection limit of 10, 25, and 10 U l⁻¹, respectively. The effect of bovine CA II (bCAII) was evaluated in the presence of 500 U l⁻¹ of each decarboxylase, showing a marked increase of the rate of the decarboxylation reaction. These results suggest that (i) CA can be used to enhance the performance of decarboxylase-based biosensors, and (ii) it possibly plays further physiological roles, acting synergistically, at specific cellular and subcellular sites, with low-activity decarboxylating enzymes.

Electrostimulations of cells by weak electric or electromagnetic LF and HF-fields are applied widely today; capacitively or inductively coupled, however, they are seldom applied for cell-free and membrane-free solutions of enzymes. First, the detection of a response of the cells (`electrical window') is a prerequisite for testing at least three parameters: frequency, amplitude and treatment time, besides reproducible biological conditions. The `state-of-the-art' of this fast developing direction of bioelectrochemistry can be characterized in the following way: the results from several laboratories of (a) cell proliferation, (b) ion transport, (c) activation of several enzymes (Na,K-ATPase), (d) increase of certain protein concentrations (heat-shock protein hsp70) are more or less in agreement. Unfortunately, there are discrepancies between no less than 7 labs in the gene expression of c-myc, c-fos histone 2B, -actin, URA-3 and others, especially for low fields (<0.05 mT), e.g., in HL60 cells! The reason why seems to be: (1) differences in the most suitable isolation procedure, (2) interferences in the case of too low magnetic flux and (3) too small ranges of parameters have been measured. Today, three open problems must be pointed out: (A) What is the physiological causality for specific `electrical windows' and their positive or negative efficacy? (B) What are the biochemical targets for either magnetic or electric fields or both? (C) What is the influence of electrical and (or) thermal noise on field efficiency?

The membrane potential (U_m), the main factor of the excitation–contraction coupling, of human allantochorial placental vascular smooth muscle cells (VSMCs) has been previously shown to depend on voltage-sensitive K⁺ channels. These channels were blocked by high external K⁺. To characterize other channels which regulated U_m, various constrictor or/and vasodilators and channel blockers were used. Serotonin depolarized VSMCs, in normal medium, but induced a more marked depolarization in VSMCs predepolarized by high external K⁺. This depolarization was inhibited by nifedipine, a blocker of voltage-gated Ca²⁺ channels. Acetylcholine, sodium nitroprusside (without effect on U_m in normal medium), hyperpolarized the predepolarized-high K⁺ medium VSMCs. This hyperpolarization was inhibited after addition of charybotoxin (a blocker of Ca²⁺-activated K⁺ channels) or/and glibenclamide (a blocker of ATP-sensitive K⁺ channels). A similar effect was obtained with isoproterenol. These results indicated that membrane potential of human placental allantochorial VSMCs was regulated by voltage-gated, Ca²⁺- and ATP-sensitive K⁺ channels and by voltage-dependent Ca²⁺ channels.

Inspired by the dissipative quantum model of brain, we model the states of neural nets in terms of collective modes by the help of the formalism of Quantum Field Theory. We exhibit an explicit neural net model which allows to memorize a sequence of several informations without reciprocal destructive interference, namely we solve the overprinting problem in such a way last registered information does not destroy the ones previously registered. Moreover, the net is able to recall not only the last registered information in the sequence, but also anyone of those previously registered.

The effect of external electromagnetic field (EMF) on a percolation structure formed during phase separation in the mixed phospholipid membranes was studied by computer simulation. Decay of the percolation structure under electromagnetic radiation was detected. It was shown that oscillation regime can be realized in this system: periodic alternation of formation and decay of the percolation cluster was observed under 10 kHz EMF. The decay of the lipid domain structure in the EMF results from anomalous increase of the permittivity of the continuous fluid lipid phase in the percolation threshold region. It is proposed that detected EMF effect can influence the signal and transport processes associated with percolation properties of biomembranes.

This paper provides a consistent approach (within a one-dimensional approximation) to the description of the evolution of the microtubule length at both low- and high-density concentrations. We derive general master-type equations which are based on the key chemical reactions involved in the assembly and disassembly of microtubules. The processes included are: polymerization and depolymerization of a single protein dimer, catastrophic disassembly affecting an a piori arbitrary number of dimers, and a rescue event. Solutions of the derived equations are compared with the existing experimental data. Important conclusions linking the emergence of bell-shaped histograms with the nature of catastrophe and rescue phenomena are drawn. Finally, we briefly discuss the emergence of coherent phenomena in microtubule polymerization, i.e., a transition to collective oscillations in the assembly and disassembly effects.

Various neutral or charged surface active substances were used for testing the influence of additives on the electrofusion of barley protoplasts. It was found that neutral surface active agents DX, TAGB, Span-80 and AEO-9 could promote the electrofusion. The positively charged surface active agents Bardac 2080, Bardac 2280 and amphoteric surface active agents dodecyl-propyl betaine and CAB betaine also promote the electrofusion, but at high concentration the electrofusion efficiency will reduce. The negatively charged polymer agents Cibacron blue DX, Fluoresceinylthiocarbamoyl DX, and active surface substances K₁₂ and Carsonol TLS⁻ presented negative effect. These phenomena were discussed from the view of adsorption of additives on the membrane and the interactions between protoplasts.

In this study, we adopted several methods of MTT colorimetry, DAPI fluorimetry and ELISA to study the effects of extremely low frequency (ELF) capacitively coupled electric fields (EFs) on the metabolism of 6B1 cells. The result shows that 50 mV cm⁻¹ ELF EF (10–100 Hz) has no significant effect on proliferation, DNA synthesis and activity of succinate dehydrogenase of 6B1 cells, indicating that the effect of ELF (10–100 Hz) EF on the metabolism of 6B1 cells is not obvious. However, 50 mV cm⁻¹, 50 Hz EF significantly promotes the HBs-Ab (Hepatitis B surface antibody) secretion of 6B1 cells, implying that under this situation, EF has some distinctive effect on the outerface of 6B1 cell membrane.

A rapid recognition in the base sequence of nucleic acids is an important prerequisite toward the diagnosis of genetic diseases and their carrier states. We have developed a hybridisation method in which a fluorescently labeled oligonucleotide is used to detect point mutations in a target by a simple fluorescence lifetime analysis of the emission of the fluorescent label. We applied this method to detect the ΔF508 mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene in a model system and with biologically derived PCR product and discuss the potential generality of this method.

It is now medically recognized that sagging skin and other signs of degenerative skin conditions, such as wrinkles and age spots, are caused primarily by oxy-radical damage. Vitamin C (Vit. C), in the form of l-ascorbic acid (Asc), is the one vitamin that can accelerate wound healing, protect fatty tissues from oxidation damage, and play an integral role in collagen synthesis. It is known that the lipid-rich stratum corneum (SC) is a highly resistant barrier to chemical agents penetrating into the skin. This report describes the first feasibility study of electroporation-mediated topical delivery (EMTD) of Asc for potential cosmetic applications. Both a cream formulation (20% Asc) and a crystal suspension (33% Asc) were applied respectively to human cadaver skin and fresh surgical skin. Six exponential pulses at 60 or 100 V and pulse lengths of 2.7–30 ms were selected. EMTD was more effective on fresh human skin than on human cadaver skin. For both skin models, EMTD with cream resulted in a greater enhancement of Vit. C penetration than with suspension. The distribution of electrical fields through the SC, epidermis, and dermis is demonstrated in computer simulation. Assuming that this fresh skin model and certain experimental conditions simulate projected in vivo applications, EMTD of Vit. C may represent an alternative method to ameliorate skin aging.