Electric organs, of electrical eel

There are problems with this approach since enzymes isolated from natural sources such as the electric organ of electric eels often display low sensitivity and selectivity to the wide range of potential pesticide targets [21]. A possible solution to this is the development of a multisensor array where a variety of genetically modified acetylcholinesterases are immobilised on an array of electrochemical sensors and the responses from these are then processed via a neural network. 

Like the acetylcholine receptor channel, the sodium channel also was purified on the basis of its ability to bind a specific neurotoxin. Tetrodotoxin, an organic compound isolated from the puffer fish, binds to sodium channels with great avidity (K nM). The lethal dose of this poison for an adult human being is about 10 ng. The sodium channel was first purified from the electric organ of electric eel, which is a rich source of the protein forming this channel. The isolated protein is a single chain of 260 kd. 

Acetylcholine receptors can be prepared from a variety of excitable tissues from animals. An example is the electric organ of electric eels, a very dense concentration of excitable tissue and a source of many neuronal receptors. A number of other chemicals competitively bind with anatoxin-a for the acetylcholine receptor (e.g., nicotine, acetylcholine itself, a-bungarotoxin) and have been radiolabeled and used in receptor binding assays for anatoxin-a. 

Direct protein sequencing of the large proteins which constituted the channel was not possible both because of the very limited amount of material available and because of the not unexpected very hydrophobic nature of these membrane proteins. However short sequences from the amino terminal were obtained and these were sufficient to allow synthesis of degenerate oligonucleotide probes which were then used to probe a library of cDNA synthesized from a small quantity of mRNA extracted from the electric organ of the eel. The cDNA from the positive plasmids identified in this way was then sequenced and the primary amino acid sequence of all the subunits so obtained. 

Part of the microheterogeneity shown by isoelectric focusing of glycoproteins from the electric organ of the eel Electrophorus electricus is attributable to variations in the content of neuraminic acid. Treatment of the glycoproteins with neuraminidase reduces the number from ten to four. The microheterogeneity is due to post-translational modification of oligosaccharides on a common polypeptide backbone. 

In adult rat brain NCAM is not the only polysialylated molecule. The sodium channel glycoprotein has been reported to be polysialylated in its a subunit [59]. The significance of the negative charge on the sodium channel is not clear, but desialylation decreases the conductivity of the channel. a2,8-linked polysialic acid chains are also carried by sodium channels on the electrical organ of the eel Electrophorus electricus [184]. 

The first report of a2,8-linked polySia on the a subunit of sodium channel proteins was by James and Agnew (1987), who identified such chains on the voltage-sensitive channel from the electric organ of the eel, Electrophorus elec-tricus. The sodium channel protein appears to be the only protein in electroplax membranes that is polysialylated, suggesting the presence of a specific a2,8-polysialyltransferase for the polysialylation of this protein (James and Agnew, 1989). 

In the electric organ of fishes, a number of such stacks are connected in parallel and in series. The total voltage attains 500 V in the electric eel. A current pulse of about 0.5 A develops when this voltage appears across an external circuit (in fresh water or seawater). For the electric ray, these numbers are 60 V and 50 A, respectively. The length of such an electric pulse is comparable with the time of cell membrane excitation (i.e., 1 to 2ms, which is quite sufficient to defeat a designated victim). Some species of fish use pulses repeated at certain intervals. 

Harris, W.E. and Stahl, W.L. (1980). Oiganisation of thiol groups of electric eel electric organ Na/K ion stimulated adenosine triphosphatase, studied with bifunctional reagents. Biochem. J. 185, 787-790. 

This was the original hypothesis put forward by Lee (1970) and expanded by Ogilvie et al. (1973). Secretory products of N. brasiliensis do indeed decrease the amplitude of contractions of segments of uninfected rat intestine maintained in an organ bath, but a role for AChE in this phenomenon was discounted due to the heat stability of the parasite factor, and the inability to duplicate the effect with AChE from the electric eel (Foster et al., 1994). Subsequent investigations demonstrated that the suppression of contraction could be duplicated by a 30-50 kDa fraction of secreted products, which contained a protein of 30 kDa that was immunologically cross-reactive with mammalian vasoactive intestinal peptide (VIP). Moreover, an antibody to porcine VIP significantly reduced the inhibitory effect of parasite-secreted products on contraction in vitro (Foster and Lee, 1996). 

Fundamentally, the eel is simply a living battery. The tips of its head and tail represent the poles of the eel s battery . As much as 80 per cent of its body is an electric organ, made up of many thousands of small platelets, which are alternately super-abundant in potassium or sodium ions, in a similar manner to the potentials formed across axon membranes in nerve cells (see p. 339). In effect, the voltage comprises thousands of concentration cells, each cell contributing a potential of about 160 mV. It is probable that the overall eel potential is augmented with junction potentials between the mini-cells. 

The isolation of the nicotinic acetylcholine receptor glycoprotein was achieved almost simultaneously in several laboratories (those of Changeux, O Brien, Brady, and Eldefrawi) and was helped tremendously by the discovery that the electric organ (elec-troplax) of the electric eel (Electrophorus electricus, an inhabitant of the Amazon River) and related species, as well as the electroplax of the electric ray Torpedo tnar-morata) of the Atlantic Ocean and the Mediterranean Sea, contains acetylcholine receptors (AChR) in a much higher concentration than, for instance, in human neuromuscular endplates or brain tissue. 

Volta pile — On March 20, 1800, Alessandro - Volta, then professor of the University of Pavia sent a letter in French from Como, Lombardy to Sir Joseph Banks (1743-1820) the president of the Royal Society of London, for publication. He described a device - that he called artificial electrical organ referring to the natural electrical organ of the torpedo or electric eel - producing perpetual electrical motion. The paper was read at the Society on 26 June and published in the September issue of the Philosophical Transactions. The whole paper appeared in English in the Philosophical Magazine the same year [i, ii]. 

Studies on the mechanism of copper ATPases require highly enriched membrane preparations or purified enzyme. Naturally enriched membranes can be obtained only from specialized membrane compartments such as the sarcoplasmic reticulum or the electric organ of eels. Since copper is a toxic trace element, it is never encountered in large quantities in cells and copper ATPases are expressed at only low levels. However, the purihcation of the CopA and CopB copper ATPases of En. hirae has recently been reported (Wunderli-Ye and Solioz, in press Bissig et al., in press). Both enzymes have been shown to form acylphosphate intermediates in purihed form, reconstituted into proteoliposomes (Wunderli-Ye and Solioz, in press Wyler-Duda and Solioz, 1996). Acylphosphate formation has also been demonstrated for the human Menkes ATPase in native membrane vesicles (Solioz and Camakaris, 1997). Further mechanistic details are, however, not available. 

The nicotinic acetylcholine receptor (NAR) is the most widely studied receptor ion channel. This is due to a very practical reason - availability. The receptor can be isolated in high yield from electric eel or electric ray, both of which use strong electric discharges to incapacitate their prey or for defence. In the electric organs of these fish, the receptor occurs in abimdance in stacks of excitable cells (Figure 9.2). Importantly, however, the NAR and voltage-gated ion channels only occur on one side of the cell. 

The availability of purified protein enabled Shosaku Numa and coworkers to clone and sequence the cDNA for the sodium channel from the electroplax cells of the eel electric organ and then from the rat. Subsequently, a large number of sodium channel cDNAs have been cloned from other sources, and sequence comparisons have been made. 

Figure 1 Subunit structure of the multiple molecular forms of ChEs. G, globular forms A, asymmetric forms with collagen-like tails. Each circle is a catalytic subunit disulfide bridges indicated by S-S as found in the electric organ of the electric eel. (Modified from Brimijoin WS (1992) US EPA Workshop on Cholinesterase Methodologies.)...

It has already been mentioned that there are some doubts A26) about the existence of an anionic site in human or horse cholinesterase. Comparative kinetic studies using a series of pyridylcarbinol acetates as substrates have shown that acetylcholinesterase from T. marmorata electric organ and the plasma cholinesterases from horse and man have similar esteratic sites. It was also shown that the electric eel organ enzyme has an anionic site, whereas the second site of butyrylcholine... 

The earlier doubts about the validity of the receptor concept may have been totally dispelled by the isolation from the electric eel, the fairly pure, nonenzymic protein receptor for acetylcholine. The properties, including kinetics, were close to those exhibited by the intact electroplax (the eel s electric organ) from which the receptor was isolated. Other receptors have since been isolated. 

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