Non-Productive Binding of Substrates as One of Aspects of Substrate Specificity of Cholinesterases of Different Origin

Taking into account the phenomenon of non-productive binding of substrate, kinetic parameters of hydrolysis of acetylcholine (ACh) and its 13 derivatives with different structures of ammonium group by cholinesterase (ChE) of human erythrocytes, ChE of horse blood serum, and ChE of optic ganglia of the Pacific squid Todarodes pacificus are determined. A dependence is revealed of values of parameters of their enzymatic hydrolysis and parameters of the non-productive binding on the substrate structure and ChE nature. Effects of salts, LiCl, NaCl, KCl, MgCl₂, CaCl₂ and BaCl₂, on various kinetic parameters, including parameters of the non-productive binding of substrate, of enzymatic hydrolysis of iodides of ACh and N-acetoxyethylene-N-ethylpiperidinium under action of horse blood serum ChE are studied. Addition of the salts to the reaction mixture produced different effects on values of the catalytic center activity (a _c) and the Michaelis constant (K _M), depending on the cation nature and the substrate structure. At the same time, values of the a _c/K _M ratio that characterize to a degree the substrate affinity to the enzyme are equal to each other for two substrates differing in structure, regardless of the presence and nature of the studied cations. Parameters of the non-productive binding of N-acetoxyethylene-N-ethylpiperidinium iodide also depended on the salt nature; however, in that case, a question arises as to the correctness of the comparative analysis, when at determinations of the parameters the non-productive binding of ACh is ignored.     

Comparative Enzymologic Study of Catalytic Properties of Brain Cholinesterase of the Mink Mustela vison

Study of preparations of different parts of brain of the American mink Mustela vison Bris. has revealed the highest activity of acetylcholinesterase (AChE) in the caudate nucleus. Using the method of substrate-inhibitor analysis, homogeneity of this AChE preparation has been shown. Acetylthiocholine was hydrolyzed with the highest rate to exceed even acetylcholine, its advantage being also revealed in a _c/K _M value that reflects to a degree the affinity of the substrate to the enzyme. The study of inhibitory specificity showed no differences of AChE in the human brain and in erythrocytes.     

Use of Bis-Alkaloid Derivatives of Dicarboxylic Acids on the Basis of Lupinine, Anabasine and Cytisine as Reversible Inhibitors of Cholinesterases of Different Origin

Comparative study was carried out on action of a group of bis-alkaloid derivatives (on the basis of lupinine, anabasine, and cytosine, and their iodomethylates) of dicarboxylic acids (succinic, glutaric, azelaic, sebacic) on activity of cholinesterase of optical ganglia of the Commander squid Berryteuthis magister from different zones of habitation in the northwest part of the Pacific Ocean as well as human erythrocyte acetylcholinesterase and horse serum butyrylcholinesterase. These compounds turned out to be potent reversible inhibitors with specificity of action with respect both of sensitivity of the studied enzymes to them and of the type of their inhibitory action. The studied inhibitors can be used as tools in biochemical taxonomy to determine populational structure of such a marketing species as the Commander squid Berryteuthis magister.     

Comparative Enzymologic Study of Catalytic Properties of Blood Serum Cholinesterase of the American Mink Mustela vison

Comparative enzymologic study of catalytic properties of cholinesterase (ChE) in blood serum of the American mink Mustela vison Schr. has revealed several peculiarities of this enzyme. First, using the method of substrate–inhibitor analysis, homogeneity of the ChE preparation has been established, i.e. only one ChE has been found in mink serum. Second, the rate of acetylcholine hydrolysis was higher than of thiocholine substrates, among which propionylthiocholine was hydrolyzed at the highest rate. Third, propionylthiocholine had the highest V/K _M value that reflects to a degree affinity of the substrate to enzyme. Fourth, the phenomenon of substrate inhibition, which is not inherent for mammalian serum cholinesterases, is revealed and kinetically analyzed. Fifth, study of inhibitory specificity has not revealed differences of the mink serum ChE from other serum ChE.