1,720,977 research outputs found
Electron transfer in nanobiodevices
Full text linkThe present tutorial is aimed at introducing the reader to the main aspects of electron transfer in nanobiodevices. Nanobiodevices are faced both from scientific and technological viewpoints and their particular implementation as electron transfer devices provides the opportunity of presenting fundamentals of electron transfer theory. Examples of implementations of stand alone devices, along with those involving reconfigurable set-ups based on an electrochemical scanning tunneling microscope, enable introducing heterogeneous electron transfer and electron transport theories in electrochemical environment. Specific cases of nanobiodevices involving redox metalloproteins are reported and experimental results are interpreted and discussed in view of the most recent theoretical advancements, in order to provide the reader with a comprehensive view of the results and promises in this exciting branch of nanotechnology
EC-STM/STS of Redox Metalloproteins and Co-factors
No full textThis chapter is intended to review some of the main experimental and theoretical results in the field of single molecule characterization of the electron transport through redox adsorbates. Both redox metalloproteins and co-factors have been object of intense investigation by EC-STM/STS techniques. Particularly, the paradigmatic case of the redox metalloprotein azurin and of derivatized quinone molecules adsorbed on atomically flat gold provide a valuable insight into the potential of the technique and into the attainable level of understanding of the electron transfer phenomenon. The results are discussed critically in view of their impact on the field of Molecular Electronics
Electrochemical scanning tunneling microscopy and spectroscopy for single-molecule investigation
No full textThe technique of electrochemical scanning tunneling microscopy (ECSTM) and spectroscopy (ECSTS) for studying electron transport through single redox molecules is here described. Redox molecules of both biological and organic nature have been studied by this technique with the aim of understanding the transport mechanisms ruling the flow of electrons via a single molecule placed in a nanometer-sized gap between two electrodes while elucidating the role of the redox density of states brought about by the molecule. The obtained results provide unique clues to single-molecule transport behavior and support the concept of single-molecule electrochemical gating
Changes in single K+ channel behavior induced by a lipid phase transition
No full textMembrane protein activity is affected by the properties of the lipid bilayer hosting them. These properties are established by both the lipid composition and the thermodynamic state of the bilayer. In the latter case, any parameter that can alter the state of the bilayer is indirectly able to affect the activity of membrane proteins. In a recent study, we have demonstrated that the activity of the KcsA ion channel is strongly related to the thermodynamic state of the lipid bilayer. In particular, when the lipid bilayer is in its main phase transition region, the conductivity of KcsA is increased and all its characteristic times change according to the characteristic times of the lipid bilayer. We propose here that the lipid bilayer can affect the distribution among many conformational substates of the open channel, affecting the corresponding channel conductivity
Model Bio‐Membranes Investigated by AFM and AFS: A Suitable Tool to Unravel Lipid Organization and their Interaction with Proteins
No full textThe study of the biological membrane has largely benefitted from the exploitation of
model bilayer systems. These simplified models of the complex biological membrane
composed of thousands of different types of molecules allow both to understand basic
physical principles underlying the membrane functioning and to test new techniques that will
be subsequently applied to biological membranes. Here we concentrate on one of the most
used model systems for this kind of investigations: the Supported Lipid Bilayer (SLB). In particular, we analyze the possibilities of investigation offered by Atomic Force Microscopy and Spectroscopy (AFM/AFS) on this model system. We discuss the information that this techniques is able to provide on the phase behavior of the lipid bilayers and on the partitioning of membrane proteins relative to the bilayer lateral heterogeneity. We discuss also the possibility to characterize the mechanical properties of lipid bilayers on the nanometer scale lateral resolution
Unravelling single metalloprotein electron transfer by scanning probe techniques
No full textThis review is intended to account for the experimental and theoretical achievements obtained in a period of about 15 years on the investigation of the electron transport through single redoxmetalloproteins by scanning probe techniques. A highly focussed research effort has been deployed by the scientists active in this particular field towards measuring and interpreting electronic current signals flowing via blue copper, redox metalloproteins (e.g. azurin). The field has taken a remarkable advantage of the use of electrochemically assisted scanning tunnelling microscope (EC-STM) which has allowed to probe single molecule signals under full control of all the potential values involved in the experiments. This experimental activity has both triggeredmore comprehensive theoretical interpretations and has been, in its turn, stimulated by theoreticians to test always new predictions. The authors hope to have succeeded in providing the reader with a valuable appraisal of this fascinating field
Effects of neurosteroids on a model membrane including cholesterol: A micropipette aspiration study
No full textAmphiphilic molecules supposed to affect membrane protein activity could strongly interact also with the lipid component of the membrane itself. Neurosteroids are amphiphilic molecules that bind to plasma membrane receptors of cells in the central nervous system but their effect on membrane is still under debate. For this reason it is interesting to investigate their effects on pure lipid bilayers as model systems. Using the micropipette aspiration technique (MAT), here we studied the effects of a neurosteroid, allopregnanolone (3α,5α-tetrahydroprogesterone or Allo) and of one of its isoforms, isoallopregnanolone (3β,5α-tetrahydroprogesterone or isoAllo), on the physical properties of pure lipid bilayers composed by DOPC/bSM/chol. Allo is a well-known positive allosteric modulator of GABAA receptor activity while isoAllo acts as a non-competitive functional antagonist of Allo modulation. We found that Allo, when applied at nanomolar concentrations (50-200 nM) to a lipid bilayer model system including cholesterol, induces an increase of the lipid bilayer area and a decrease of the mechanical parameters. Conversely, isoAllo, decreases the lipid bilayer area and, when applied, at the same nanomolar concentrations, it does not affect significantly its mechanical parameters. We characterized the kinetics of Allo uptake by the lipid bilayer and we also discussed its aspects in relation to the slow kinetics of Allo gating effects on GABAA receptors. The overall results presented here show that a correlation exists between the modulation of Allo and isoAllo of GABAA receptor activity and their effects on a lipid bilayer model system containing cholesterol
Going 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
Effect of neurosteroids on a model lipid bilayer including cholesterol: An Atomic Force Microscopy study
No full textAmphiphilic molecules which have a biological effect on specific membrane proteins, could also affect lipid bilayer properties possibly resulting in a modulation of the overall membrane behavior. In light of this consideration, it is important to study the possible effects of amphiphilic molecule of pharmacological interest on model systems which recapitulate some of the main properties of the biological plasma membranes. In this work we studied the effect of a neurosteroid, Allopregnanolone (3α,5α-tetrahydroprogesterone or Allo), on a model bilayer composed by the ternary lipid mixture DOPC/bSM/chol. We chose ternary mixtures which present, at room temperature, a phase coexistence of liquid ordered (Lo) and liquid disordered (Ld) domains and which reside near to a critical point. We found that Allo, which is able to strongly partition in the lipid bilayer, induces a marked increase in the bilayer area and modifies the relative proportion of the two phases favoring the Ld phase. We also found that the neurosteroid shifts the miscibility temperature to higher values in a way similarly to what happenswhen the cholesterol concentration is decreased. Interestingly, an isoform of Allo, Isoallopregnanolone (3β,5α -tetrahydroprogesterone or isoAllo), known to inhibit the effects of Allo on GABAA receptors, has an opposite effect on the bilayer properties
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