Showing papers on "Acetylthiocholine published in 1969"
TL;DR: T theoretical equations were derived for an enzyme with two binding sites to both of which substrate and inhibitor can combine, and it was shown that haloxon combines with a site involved in inhibition by substrate.
Abstract: 1. The kinetics of the reaction of di-(2-chloroethyl) 3-chloro-4-methylcoumarin-7-yl phosphate (haloxon) and related compounds with acetylcholinesterase were studied and found to be unusual. 2. By a progressive reaction haloxon produces a di-(2-chloroethyl)phosphorylated enzyme. The influence of substrate on this reaction leading to a phosphorylated active centre was studied. From competition experiments between inhibitor and substrate values of Km for acetylcholine and acetylthiocholine of 0·79mm and 0·23mm respectively were derived. 3. Haloxon also combines with acetylcholinesterase by a non-progressive reaction, producing a complex that is reversible by dilution and by high concentrations of acetylcholine and acetylthiocholine. From this non-progressive reaction the competition between haloxon and substrate was studied, and it was shown that haloxon combines with a site involved in inhibition by substrate. From competition experiments the following dissociation constants were derived: for combination of haloxon and this site Ki is 4·9μm and for the combination of substrates with this site K88 values are 12mm and 3·3mm for acetylcholine and acetylthiocholine respectively. 4. The non-phosphorus-containing compound 3-chloro-7-hydroxy-4-methylcoumarin was shown to be a good reagent for the site involved in inhibition by substrate; its dissociation constant for the combination with this site is 30μm. 5. In order to interpret the experimental results, theoretical equations were derived for an enzyme with two binding sites to both of which substrate and inhibitor can combine. The equations correlate the activity of the enzyme with the concentration of substrate and inhibitor, for both progressive and non-progressive inhibition. These equations are applicable to reactions of acetylcholinesterase with organophosphorus compounds, carbamates etc. and may be applicable to other enzymes possessing two binding sites.
77 citations
TL;DR: Observations and other biochemical and pharmacological data suggest the involvement of the acetylcholine system in conduction of impulses along lobster nerves, which is similar to those seen in neuromuscular junctions.
38 citations
TL;DR: The existence of isoenzymes of ACHE with different enzymatic properties is discussed and two of them could be characterized by measurement of their Km value and Iso for some inhibitors.
15 citations
TL;DR: AChE has been localized at the neuromuscular junctions of the rat diaphragm in an electron microscope histochemical investigation, and is associated with the pre- and postsynaptical membranes, with much greater activity at the latter.
Abstract: By means of a quaternary carbon analogue of acetylthiocholine (AThCh)' 3,3-dimethylbuthylthioacetate (DMBTA) as a substrate for cholinesterase (ChE), acethylcholinesterase (AChE) has been localized at the neuromuscular junctions of the rat diaphragm in an electron microscope histochemical investigation. AChE is associated with the pre- and postsynaptical membranes, with much greater activity at the latter. Enzymatic activity is not found within the junctional clefts, nor in association with the synaptic vesicles of the axonal end arborization. The lack of AChE in association with the vesicles is regarded as particularly important, since DMBTA due to its electroneutrality probably penetrate biological membranes more easily than charged substrates employed so far.
4 citations