[Significance of the dopamine-blocking and m-choline-blocking components in the antiapomorphine action of neuroleptics]. / Znachenie dofaminoblokiruiushchego i m-kholinoblokiruiushchego komponentov v antiapomorfinovom deistvii neiroleptikov.

In experiments on rats and mice the correlation between the ability of neuroleptics to antagonize apomorphine induced stereotypy and to block central dopamine and muscarinic acetylcholine receptors was studied. The analysis showed significant correlation (v = 0.76; P less than 0.05) between antistereotypic effects of drugs and their ability to inhibit 3H-spiperone binding to rat striated tissue. However, no correlation was found between antistereotypic effect of neuroleptics and their ability to block 3H-quinuclidinyl benzylate binding or arecoline-induced tremor.

[Solubilization by various detergents, of the muscarinic cholinoreceptor and its complex with quinuclidinyl benzilate]. / Soliubilizatsiia nekotorymi detergentami muskarinovogo kholinoretseptora i ego kompleksa s khinuklidinilbenzilatom.

The possibilities to solubilize the rat brain cortex muscarinic acetylcholine receptor and its complex with [3H]-L-quinuclidinyl benzilate (QNB) were studied, using 14 detergents. It was shown that the native muscarinic cholinoreceptor was solubilized in addition to digitonin, also by CHAPS, with a 6% yield. Besides, the receptor-QNB complex was solubilized with the detergents Triton X-100, -102, -114, -165 (with 30% and 50% yields) and within a narrow concentration range with sodium dodecyl sulfate (50% yield). Some detergents of the Tween series, e.g., Triton X-45 and -305, as well as sodium deoxycholate and sodium oxycholate, did not solubilize the native receptor and its complex with QNB. It was found that yield of receptor solubilization did not exceed half of the total number of the receptor sites in the membranes, despite the fact that different concentrations of detergents were applied. The solubilization yield did not increase, when different mixtures of detergents were used. It was assumed that incomplete solubilization of the receptor protein reflects its heterogeneity in the membrane structure.

[Kinetics of the inactivation of muscarinic cholinoreceptors by solubilized digitonin]. / Kinetika inaktivatsii soliubilizirovannogo digitoninom muskarinovogo kholinoretseptora.

The kinetics of spontaneous inactivation of the digitonin-solubilized rat brain muscarinic cholinoreceptor was investigated at 4 degrees, 15 degrees, 25 degrees, 35 degrees and 45 degrees C. The inactivation process was followed by the loss of specific L-[3H] quinuclidinyl benzilate binding capacity after incubation of the receptor at an appropriate temperature. Since the inactivation process of the receptor inactivation obeys the first order kinetics, it was possible to determine the values of inactivation rate constants (kappa in). It was shown that the inactivation rate does not depend on the detergent excess in a reaction mixture and is characterized by the apparent activation energy, Ea = 158 +/- 7 . KJ/mole and entropy, delta S not equal to = 249.8 J/K . mole. These values are in good agreement with those obtained for the water-soluble proteins, but differ essentially from the analogous values for the spontaneous activation of the membrane-bound receptor.

[Effect of pH on the cholinesterase hydrolysis of different substrates]. / Vliianie pH na gidroliz kholinesterazoi razlichnykh substratov.

The effect of pH on the kinetic constants of cholinesterase-catalyzed hydrolysis of isoamylacetate and acetylthiocholine was investigated. For the first substrate the rate-limiting step is the enzyme acetylation reaction, while the overall hydrolysis rate of the second substrate is limited by the deacetylation reaction. It was concluded that a basic group is involved in the deacetylation reaction and in the non-covalent binding step of both ionic and non-ionic substrates. An acidic group participates in the both reaction steps. It was suggested that protonation of the basic group leads to a conformational transition of the free enzyme and can also participate in the catalytic mechanism. The second basic group characterized by Ka3 can be the functional group of the enzyme anionic site. Taken together, the influence of pH on cholinesterase catalysis can be generalized by the overall reaction scheme.

[Acetylcholinesterase of cobra venom. Determination of concentration of active sites]. / Atsetilkholinesteraza iada kobry. Opredelenie kontsentratsii aktivnykh tsentrov

O-Nitrophenyl dimethylcarbamate and organophosphorus inhibitors O-n-propyl-p-nitrophenyl methylphosphonate, O-n-butyl-p-nitrophenyl methylphosphonate, O,O-diethyl-p-nitrophenyl phosphate, O-n-butyl-S-(beta-ethylmercaptoethyl) methylthiophosphonate, methysulphate of O,O-diethyl-S-(beta-phenyldimethylammoniumethly) thiophosphate were used in the titration of acetylcholinesterase active site concentratration in Naja naja oxiana venom. No side reactions with the acetylcholinesterase molecule as well as with other components of the venom were observed. In titration the effective concentrations of organophosphorus inhibitors with asymmetric phosphorus were 50% of their analytical concentrations, since cobra venom cholinesterase showed practically absolute stereoselectivity against the compounds.