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S Tucek

Publications and source records attributed to S Tucek.

121 records · Page 7Linked to original sources
PubMed1967

The use of choline acetyltransferase for measuring the synthesis of acetyl-coenzyme A and its release from brain mitochondria.

1. A method for measuring small amounts of acetyl-CoA synthesized in subcellular fractions of the brain from pyruvate and released from particles into the incubation medium has been developed by using placental choline acetyltransferase and choline in the incubation medium to transform acetyl-CoA into acetylcholine. Acetylcholine is measured by biological assay. Optimum conditions of incubation are described. 2. With fresh mitochondria, a decrease of acetyl-CoA output into the medium is observed in the presence of ATP or ADP, and an increase in the presence of calcium chloride or 2,4-dinitrophenol. Fluorocitrate and malonate have little or no effect. 3. After the mitochondria had been treated with ether, the release of acetyl-CoA into the medium is much larger; presumably, nearly all acetyl-CoA synthesized is then released and transformed into acetylcholine under the conditions used. The release of acetyl-CoA is diminished in the presence of Krebs-cycle intermediates and ADP. 4. Of all subcellular fractions, the highest acetyl-CoA production from pyruvate is found in the crude mitochondria; rates up to 51 mumoles of acetyl-CoA/g. of original tissue/hr. are observed in ether-treated samples. 5. The activities of acetyl-CoA synthetase and ATP citrate lyase found in homogenates and nerve-ending fractions of brain tissue are considerably lower than those of pyruvate oxidase complex and choline acetyltransferase. 6. The bearing of some of the findings on the question of the source of acetyl radicals for the synthesis of acetylcholine in vivo is discussed.

Acetylcholine↗
PubMedDate not supplied

Positive allosteric action of alcuronium on solubilized cardiac muscarinic receptors.

Alcuronium was found earlier to increase the binding of (3H)methyl-N-scopolamine [(3H)NMS] to muscarinic receptors in membranes of rat heart atria by increasing the receptors' affinity for (3H)NMS, without altering the number of (3H)NMS binding sites. We have now investigated how the interaction of alcuronium with muscarinic receptors is affected by solubilization. In experiments on pig heart atria, alcuronium had a positive allosteric effect on (3H)NMS binding both to unsolubilized receptors and to receptors solubilized by digitonin and deoxycholate. The cooperativity coefficient alpha was 0.39 +/- 0.01 for unsolubilized and 0.57 +/- 0.01 for solubilized receptors. Under the conditions used for solubilization, muscarinic receptors did not interact with G proteins, as indicated by experiments with the binding of carbachol in the absence and presence of a stable GTP analogue. Alcuronium slowed down the rates of (3H)NMS association with, and dissociation from, solubilized receptors; the dissociation rate constant was diminished more than 300 times by 30 microM alcuronium. The results show that the positive allosteric action of alcuronium on cardiac muscarinic receptors and its effect on the kinetics of radioligand binding are preserved after receptor solubilization and do not depend on the interaction of receptors with G proteins.

Alcuronium↗
PubMedDate not supplied

Positive effects of allosteric modulators on the binding properties and the function of muscarinic acetylcholine receptors.

Data are reviewed indicating that allosteric modulators can enhance the affinities of muscarinic receptors for their antagonists and agonists, that the enhancement of the affinity for agonists is relevant functionally, and that the allosterically induced conformational change also affects the interaction between the receptors and the G proteins.

Allosteric Regulation↗