Electrical capacitance, protein

Casadio, R., Venturoli, G. and Melandri, B. A. (1988). Evaluation of the electrical capacitance in biological membranes at different phospholipid to protein ratios -a study in photosynthetic bacterial chromatophores based on electrochromic effects, Eur. Biophys. J., 16, 243-253. 

Since the electrical capacitance of the mitochondrial inner membrane is low, the membrane potential would be discharged by the uptake into the matrix of only about 1 nmol of Ca/mg protein if no other ions were to move across the membrane (Fig. 5). In order for further net accumulation of the cation to occur, a net extrusion of protons by either the respiratory chain or the ATP synthase is required. 

Acetylcholine receptor from electric organ of Torpedo sp. Receptor protein noncovalently bound on the surface of a planar interdigitated capacitative sensor. Response was concentration dependent and specific for ACh and inhibited by (+ )-tubocurarine, amantidine and a-neurotoxin. [66]... 

Pure lipid membranes are electrical insulators with a specific capacitance of 1 tiF/cm, which separate two electrolytic compartments. The conductance of biological membranes is maiifly determined by highly specialized proteins that act as ion chaimels. For supported membranes to mimic the electrical properties of a biological membrane, it is necessary to measure its electrical characteristics. Even very small defects that are not... 

Electrical properties of membranes. Biological membranes serve as barriers to the passage of ions and polar molecules, a fact that is reflected in their high electrical resistance and capacitance. The electrical resistance is usually 10 ohms cm, while the capacitance is 0.5-1.5 microfarad (pF) cm . The corresponding values for artificial membranes are 10 ohms cm and 0.6 - 0.9 pF cm . The lower resistance of biological membranes must result from the presence of proteins and other ion-carrying substances or of pores in the membranes. The capacitance values for the two types of membrane are very close to those expected for a bilayer with a thickness of 2.5 nm and a dielectric constant of 2. 4 The electrical potential gradient is steep. 

In electrically permeabilized insulin-secreting cells, the influence of soluble second messengers on exocytosis can be studied directly, since it is possible to dialyze such cells with respect to nucleotides and ions while cytosolic proteins are retained. In the presence of ATP, Ca " stimulates insulin exocytosis with an EC50 of approximately 1.6 l/Vl (Vallar efal., 1987, Ullrich efal., 1990). This is in close agreement with the value for Ca -stimulated exocytosis in patch-clamped mouse P-cells obtained using the capacitance method (Bokvist ef al.,... 

At frequencies below 63 Hz, the double-layer capacitance began to dominate the overall impedance of the membrane electrode. The electric potential profile of a bilayer membrane consists of a hydrocarbon core layer and an electrical double layer (49). The dipolar potential, which originates from the lipid bilayer head-group zone and the incorporated protein, partially controls transmembrane ion transport. The model equivalent circuit presented here accounts for the response as a function of frequency of both the hydrocarbon core layer and the double layer at the membrane-water interface. The value of Cdl from the best curve fit for the membrane-coated electrode is lower than that for the bare PtO interface. For the membrane-coated electrode, the model gives a polarization resistance, of 80 kfl compared with 5 kfl for the bare PtO electrode. Formation of the lipid membrane creates a dipolar potential at the interface that results in higher Rdl. The incorporated rhodopsin may also extend the double layer, which makes the layer more diffuse and, therefore, decreases C. ... 

In the present system with the copper-2% zinc electrodes, all three processes of protein adsorption, charge transfer, and Faradaic oxidations and reductions are possible. The peaks observed in the anodic and cathodic processes are related, respectively, to oxidations and reductions of the electrode. Copper oxides, chlorides, basic chlorides, phosphates, etc., as well as zinc products, are probable compounds for these electrochemical reactions. Increased Faradaic processes and charge transfer processes with protein solutions are factors for increasing the j-U profiles at U s less than +0.3 V. Since the sweep rate is a constant here, the capacitance of the double layer must increase for the protein solutions, if the increase in j is not all due to Faradaic processes One analog of the electrical double layer capacitance incorporates three capacitors in series (44). Hence... 

Liquids that are highly aerated and/or contain high protein concentration are often susceptible to foaming, which may interfere strongly with the bioprocess in question. The amount of foam can be measured with sensors based on electrical conductivity, heat conductivity, capacitance, or light scattering [41],... 

Capacitance, C, provides direct information on the structure of the adsorbed layer (10, 11). The change in the differential capacity of the electrical double layer between a polarized mercury surface and a 0.15 M NaCl solution containing various concentrations of protein... 

The development of the concept of ionic channel started with the realisation by Bernstein that cellular excitability was a property of the membrane. The starting point at the experimental level was the observation by Cole and Curtis that, concomitant with a propagated electrical impulse (manifestation of cellular electrical excitability) in the squid giant nerve fibre, a decrease in the electrical resistance took place with no detectable change in the membrane capacitance. This result lent strong support to Bernstein s concept and clearly indicated that the most plastic components of the axolemma, the proteins, underwent structural transitions leading to a transient increase in ionic fluxes. 

For example, it is known that proteins are important membrane constituents the ratio by weight of proteins to lipids varies between 1.5 1 and 4 1 for different membranes. Since the bulk of the membrane capacitance is associated with the lipid phase, the constancy of the membrane capacitance during the passage of an electrical impulse may be interpreted assuming that only a minute fraction of these proteins (a few molecules scattered throughout within the nerve membrane) underwent transitions inducing dramatic changes in conductivity. 

The nerve cell membrane, which is about 5 nm thick, consists primarily of lipids and proteins. When at rest it is permeable basically to potassium ions (although its resistance in this state is rather high, ca. 10 fl cm ), and therefore the electric potential difference between the inner and outer solutions (this difference is called the membrane potential or simply the potential) is negative at rest and amounts to a few tens of mV (about -60 mV on the giant axon). The membrane capacitance is of the order of 1 /iF/cm. Thus a neuron membrane is already polarized when at rest. If some external action shifts the potential from its value at rest to more negative values (its absolute value increasing), the resultant situation is usually called hyperpolarization. Potential shift in the positive direction is called depolarization. If the potential reverses its sign and becomes positive the term is overshoot. ... 

Although it is known that the lipid composition of cell membranes determines membrane fluidity as well as the function and activity of membrane-bound proteins and enzymes (24), it is not known what effect changes in the relative proportions of specific fatty acids of phospholipids have on the capacitive properties of membranes. The maintenance of an electrical potential across membranes is essential to cell function and survival and may be altered in severe disease states (25). 

Soy protein dust requires 0.06 J for ignition. A belt moving the material has a capacitance of 300 pF. How many volts of electrical potential must accumulate on the belt to reach sufficient energy for ignition ... 

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