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Biomedical subjects

M E Eldefrawi

Publications and source records attributed to M E Eldefrawi.

At least 145 records · Page 8Linked to original sources
PubMed1972

Macromolecules from lobster axon membranes that bind cholinergic ligands and local anesthetics (recpetors-procaine-acetylcholine-nicotine-Na + and K + gates).

The technique of reversible equilibrium dialysis has been applied to the study of macromolecules that are essential for axonal conduction. A binding component from a preparation of an axon-plasma membrane has been characterized and shown to bind nicotine with a K(D) = 0.42 +/- 0.04 muM and to the extent of 0.7 nmol/g of wet nerve. This binding was competitively blocked by acetylcholine (K(i) = 43 +/- 7 muM) and procaine (K(i) = 2.9 +/- 0.2 muM). This axonal macromolecule exhibits several of the properties of cholinergic postsynaptic receptors including its concentration in the tissue, blockade of its binding of nicotine by cholinergic drugs and alpha-bungarotoxin, and its phospholipoprotein nature. Some important differences are a lower affinity for acetylcholine and its binding of procaine. It is suggested that this nicotine receptor is on the internal surface of the axon plasma membrane and is a component common to both the Na(+) and K(+) gates.

Acetylcholine↗
PubMed1972

Characterization and partial purification of the acetylcholine receptor from Torpedo electroplax.

Binding of acetylcholine in the concentration range 1 nM-1 muM was measured by equilibrium dialysis to a particulate preparation of Torpedo electroplax, without or with prior treatment of the tissue with one of three chemical modifying reagents. Significant reduction in binding of acetylcholine resulted after treatment with 1,4-dithiothreitol, p-chloromercuribenzoate, or p-(trimethylammonium)-benzenediazonium fluoroborate. Partial reversal of the reduction in binding occurred when dialysis was performed in the presence of 5,5'-dithiobis-(2-nitrobenzoic acid) or potassium ferricyanide (in the case of treatment with dithiothreitol), and 2-mercaptoethanol (in the case of treatment with p-chloromercuribenzoate). It is concluded that the functional acetylcholine-receptor macromolecule of Torpedo electroplax has disulfide bond(s), sulfhydryl group(s), and one or more of the amino acids vulnerable to diazotization by p-(trimethylammonium)-benzenediazonium fluoroborate. This, plus the effect of phospholipase C (EC 3.1.4.3) in elimination of detectable binding of acetylcholine after electrofocusing, is additional evidence that the functional acetylcholine receptor is a phospholipoprotein or a phospholipid-protein complex, which has a low isoelectric point of 4.5 +/- 0.2, yet is denatured by exposure to low pH for 24 hr. Due to this adverse effect, recovery of binding of acetylcholine after electrofocusing, as detected by equilibrium dialysis or ultrafiltration, is only 23% and, so far, only 6.3-fold purification of functional acetylcholine receptors by this technique is possible. Three or two forms of acetylcholinesterase (EC 3.1.1.7), whose peaks have isoelectric points ranging from 4.3 to 7.2, appear after electrofocusing of Torpedo extracted with 1% Triton X-100 or Lubrol, respectively. The major peak in either preparation has an isoelectric point of 5. Although the peaks of the functional acetylcholine receptors and of acetylcholinesterase of Torpedo electroplax are separable by electrofocusing, it has not been possible to isolate fractions that contain functional receptors but that are free of acetylcholinesterase. The opposite is possible.

Acetylcholine↗
PubMed1971

Acetylcholine binding to Torpedo electroplax: relationship to acetylcholine receptors.

Binding of [(3)H]acetylcholine to a particulate fraction of Torpedo electroplax was measured by equilibrium dialysis. Two high-affinity sites present on phospholipoproteins bound acetylcholine reversibly, and binding was blocked by nicotinic drugs. Characteristics of this binding suggest that these phospholipoproteins may be acetylcholine receptors.

Acetylcholine↗
PubMed1971

Binding sites for cholinergic ligands in a particulate fraction of Electrophorus electroplax.

The binding of four radioactive cholinergic ligands to a particulate fraction of Electrophorus electricus electroplax was investigated by equilibrium dialysis and found to be reversible. A single site (concentration, 0.02-0.03 nmol/g electroplax) that bound muscarone and nicotine was found to be on a phospholipoprotein; it is suggested that this is the acetylcholine receptor. Four binding sites for decamethonium were found; the highest-affinity site (0.03 nmol/g) may be the same one that binds muscarone and nicotine, both because of the chemical nature of the binding macromolecule and because decamethonium competes with muscarone and nicotine in binding. Dimethylcurare bound to three sites. The lower-affinity sites appeared to be on different macromolecules.When binding of the four cholinergic ligands (at 0.01 muM) to 28 arbitrarily selected proteins was determined, it was concluded that muscarone would be the most specific for the acetylcholine receptor, in that it bound to none of the 28 proteins tested; nicotine bound to one, dimethylcurare to two, and decamethonium to ten of the proteins. Nicotine or muscarone appear to be the ligands of choice in studying binding to the acetylcholine receptor; decamethonium appears to have inadequate specificity.

Acetylcholine↗
PubMed1971

Autoinhibition of acetylcholine binding to Torpedo electroplax; a possible molecular mechanism for desensitization.

Binding of [(3)H]acetylcholine (measured by equilibrium dialysis) to a particulate preparation of Torpedo electroplax exhibits autoinhibition at concentrations higher than 1 muM. It is suggested that autoinhibition results from acetylcholine binding to regulatory sites on its receptor macromolecules. This binding causes the change to a new and inactive conformation and rejection of acetylcholine bound to the larger number of active sites. The relationship to the physiological phenomenon of desensitization is discussed.

Acetylcholine↗
PubMed1970

A muscarone-binding material in electroplax and its relation to the acetylcholine receptor. II. Dialysis assay.

An equilibrium dialysis technique, applied to lyophilized particulate fractions of Torpedo electroplax, gave data consistent with a single kind of macromolecular binding of muscarone, with binding constant, 7 x 10(-7)M and an amount of 1 nmole per gram original electroplax. The effects on muscarone binding of 38 drugs suggested that muscarone binding reflected acetylcholine receptor activity. Of 18 enzyme preparations, only trypsin, chymotrypsin, and phospholipase C reduced binding activity, suggesting that a phospholipoprotein was binding. Partial "solubilization" of the binding protein was achieved, but the "solubilized" activity did not migrate on electrophoresis. Additional evidence was provided that acetylcholinesterase was not responsible for this muscarone binding.

Acetylcholine↗
PubMed1967

Resistance of the housefly (Musca domestica L.) to insecticides in Egypt.

Housefly resistance to DDT and lindane in Egypt was first reported 17 years ago, yet these insecticides continue to be used.The present degree of housefly resistance to DDT and lindane was found to be high, and cross-resistance to dieldrin was discovered. An analysis of dieldrin resistance was made, and it was found that a single selection with dieldrin at a high selection pressure resulted in a homozygous resistant strain. The strains were found to be still susceptible to organophosphates and carbamates, some of which could be chosen for housefly control in Egypt.

Animals↗