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Z Salamon

Publications and source records attributed to Z Salamon.

14 recordsLinked to original sources
PubMed1992

Direct electrochemistry of thioredoxins and glutathione at a lipid bilayer-modified electrode.

By using direct electrochemical analysis we have established that the reduction of Escherichia coli thioredoxin (EcT), T4 thioredoxin (T4T), and glutathione (GSSG) occurs at a self-assembled lipid bilayer-modified gold electrode via two separate one-electron processes. The first electron transfer has half-wave potentials of -0.05 +/- 0.01, -0.07 +/- 0.01, and -0.06 +/- 0.01 V, whereas the second one has values of -0.48 +/- 0.01, -0.39 +/- 0.01, and -0.45 +/- 0.01 V, for EcT, T4T, and GSSG, respectively. The scan-rate dependence of the cyclic voltammetry indicates, for both waves, that the process of electron transfer is dominated by a bulk diffusion of free species to and from the electrode, and that strongly adsorbed species do not significantly contribute at the scan rates used. The voltage separation of the peak currents indicates a quasi-reversible electron transfer process with an electrochemical rate constant which is larger for the second (lower potential) electron than for the first one. Using the above half-wave potentials of the one-electron steps, one can calculate a thermodynamic half-wave potential for the two-electron reduction processes. The values of these potentials are -0.265, -0.23, and -0.25 V for EcT, T4T, and GSSG, respectively. These are in excellent agreement with literature values obtained from equilibrium measurements of enzyme-catalyzed reactions involving these species. It is quite clear from these results that lipid bilayer-modified electrodes provide a biocompatible and direct means of efficiently carrying out electrochemical reactions with sulfur-based redox systems, as we have previously shown to be the case with metalloproteins.

Electrochemistry↗
PubMed1992

Direct electrochemistry of spinach plastocyanin at a lipid bilayer-modified electrode: cyclic voltammetry as a probe of membrane-protein interactions.

The electron transfer reactions between a lipid bilayer-modified gold electrode and oxidized spinach plastocyanin have been studied by cyclic voltammetry, using either an electrically neutral phosphatidylcholine (PC) bilayer or a positively charged PC bilayer containing 40 mol% dimethyldioctadecylammonium chloride, at two ionic strengths of electrolyte (0.02 and 0.2 M NaClO4). Plastocyanin was found to interact strongly enough with the lipid membrane to support an efficient electron transfer reaction with the electrode. The interaction forces, and therefore the mode of diffusion of plastocyanin molecules to the electrode, which limits the electron transfer rate, could be controlled by the PC concentration. At low lipid concentrations (0-5 mg/ml), electrostatically attractive interactions between specific microelectroactive sites on the surface of the lipid membrane and plastocyanin molecules predominate, producing a radial mode of diffusion of the protein molecules to the electrode surface. On the other hand, at high lipid concentrations (greater than 5 mg/ml), interaction between plastocyanin and the lipid membrane occurs via hydrophobic forces, and a linear diffusion of protein molecules limits the electron transfer process. These observations support and extend other experimental and theoretical results which indicate two possible sites on the surface of the plastocyanin molecule, one hydrophobic and one negatively charged, which are able to participate in electron transfer reactions. We conclude that electrochemical measurements with the present system provide a new approach to the study of redox protein-membrane interactions.

Electrochemistry↗
PubMed1991

A self-assembled pigmented BLM on a platinum support: the light-induced electrical effects.

The light-induced voltage and current changes under continuous illumination have been investigated in pigmented self-assembled lipid bilayer membranes deposited on a platinum electrode. Such self-organized pigmented bilayer-platinum system containing Zn-Phthalocyanine (ZnPc) as a photosensitizer and glycerol-dioleate (GDO) as a bilayer forming solution has been found to shift its electrode potential to more positive value on light irradiation as well as to increase the cathodic current across the membrane. The results indicate a direct electron transfer from the platinum electrode to hydrogen ion in the electrolyte solution. Furthermore, it has also been demonstrated a dramatic increase of the photocurrent over the time course of BLM formation visualizing a role of the bulk quenching processes which are significantly diminished in thin bilayer membrane.

Diglycerides↗
PubMed1991

Lipid bilayer-based sensors and biomolecular electronics.

The lipid bilayer postulated as the basic structural matrix of biological membranes is widely accepted. Experiments in the early 1960s have made direct studies of lipid bilayers possible. At present, the planar bilayer lipid membrane (BLM) together with spherical lipid bilayers (liposomes), upon suitable modification, serves as a most appropriate model for biological membranes. In recent years, advances in microelectronics and interest in ultrathin organic films, including BLMs, have resulted in a unique fusion of ideas toward the development of biosensors and transducers. Furthermore, recent trends in interdisciplinary studies in chemistry, electronics, and biology have led to a new field of research: biomolecular electronics. This exciting new field of scientific-technological endeavor is part of a more general approach toward the development of a new, postsemiconductor electronic technology, namely, molecular electronics with a long-term goal of molecular computers. Experimental BLMs have been mainly used in the past as models of biological membranes. The methods of BLM studies may not be familiar to those outside biomedical research. Therefore, a brief description of the experimental techniques will be given in Section IV. Recently, it has been demonstrated that BLMs, after suitable modification, can function as electrodes and exhibit nonlinear electronic properties. These and other experimental findings relevant to sensor development and to "biomolecular electronic devices" (BED) will be covered in Section V, after a brief description of biomembranes which have been suggested as nature's molecular devices (Section III). In the last section, the potential use of the BLM system together with its modifications in the development of a new class of organic diodes, switches, biosensors, electrochemical photocells, and biofuel cells will be presented (Section VI). Additionally, this paper, besides presenting a review of our work and those of others on BLMs and liposomes in relation to biosensors and molecular electronics, reports a novel technique for obtaining BLMs (or lipid bilayers) on solid supports. The presence of solid support on one side of the BLM greatly enhances its mechanical stability, while retaining the dynamic properties of the lipid bilayer. Advantages of the new technique for self-assembling amphiphilic molecules on rigid substrates are discussed in terms of their possible uses. That is, the new BLM system (s-BLMs) is potentially useful for technological applications in the area of biosensors, enzyme electrodes, and molecular electronics as well as biochips (Section IV.C). The dividing line between the present microscopic and the future molecular electronics is 1 micron.(ABSTRACT TRUNCATED AT 400 WORDS)

Biological Transport, Active↗
PubMed1990

Self-assembling bilayer lipid membranes on solid support.

Solid-supported bilayer lipid membranes (s-BLMs) that possess some properties similar to those of conventional BLMs can be self-assembled on a freshly cleaved metal wire by a two-step procedure: (i) The tip of a Teflon-coated platinum wire, while immersed in a lipid solution, is cut off with a scalpel; (ii) the new tip of the wire, having become coated with lipid solution, is transferred into 0.1 M KCl. After a few minutes, a stable lipid bilayer forms spontaneously on the tip of the wire, as verified by electrical measurements. An application of such a supported BLM (s-BLM) is reported for the detection of Pb2+ ions. The s-BLM is liquid-crystalline in structure, which makes it amenable to modification for basic studies, as well as for technological applications such as biosensors and molecular electronic devices.

Lipid Bilayers↗
PubMed1976

Enhancement studies on algae and isolated chloroplasts. Part I. Variability of photosynthetic enhancement in Chlorella pyrenoidosa.

Studies of the variability of enhancement in Chlorella pyrenoidosa confirm the existence of two types of variability: a very slow diurnal variation linked to the growth cycle and a much more rapid adaptive response to the immediate incident light conditions (State I-State II transitions). Measurements of the wavelength dependencies and relative contributions of these two types of variability suggest that they may be linked. A close examination of the enhancement signals associated with the State I-State II transition reveals that the transitions can take place in any one of three ways: by a change in Photosystem II efficiency alone, by a change in Photosystem I efficiency alone or by a simultaneous change in the efficiencies of both photo systems. Measurements of the rates of transition between State I, State II and the dark adapted state, Dark, suggest that the behaviour of State II and Dark are normally, but not always, identical. The transitions between the three states were found to be first order. For those samples exhibiting the same behaviour in Dark and State II, the rate of the State I-State II transition was found to be independent of the wavelength of Light II, suggesting that the return from State I to State II is essentially a dark process and that the driving force for the adaptive transition is the over-stimulation of Photosystem I. Finally, a model is proposed, involving an antagonistic control of the quantum yields of photochemistry of the two photosystems, that is capable of explaining the links between the two types of variability, their wavelength dependencies and the shapes of the individual enhancement signals.

Chlorella↗
PubMed1976

Enhancement studies on algae and isolated chloroplasts. Part II. Enhancement of oxygen evolution in intact chloroplasts.

Intact isolated chloroplasts were shown to exhibit a characteristic three-phase pattern of development of oxygen evolution activity. The first phase, Phase I, appeared to be an equilibration phase in which the isolated chloroplasts adapted to the conditions on the electrode surface. It was characterised by a rapidly increasing rate of oxygen evolution accompanied by decreasing enhancement signals. The second phase, Phase II, was an intermediate phase in which the rate of oxygen evolution was maximal and no enhancement was observed. In the last phase, Phase III, the rate of oxygen fell again, normal enhancement was still missing, but the samples appeared to undergo slow adaptive changes closely related to the State I-State II changes previously reported for whole cell systems. The concentrations of Mg2+ within the chloroplast were shown to play an important role in the control of the development of both the oxygen evolution and enhancement signals. It was shown how these signals could be explained in terms of a model that was consistent with that developed in Part I of this investigation to account for the variability of enhancement of the alga Chlorella pyrenoidosa.

Chlorella↗