Biomedical subjects
G Blanchet
Publications and source records attributed to G Blanchet.
[Acetylcholinesterase. I. Kinetic aspects of interaction with reversible effectors].
Interaction of an effector M with acetylcholinesterase (EC 3.1.1.7) according to the model of Krupka and Laidler was analysed. Some usual functions of [M] : 1/VM, [(VO/VM)-1]/[M] (where VO and VM are the steady state rates in the absence and in the presence of modifiers, respectively), vertical intercept 1/VM, slope KM/VM and absolute value of reciprocal horizontal intercept KM of Lineweaver-Burk plots are investigated and corresponding plots described. It is particularly shown that if Dixon plots are curves concave downwards, plots of [VO/VM)-1]/[M] and 1/VM against [M] are hyperbolas concave upwards and downwards respectively. If Dixon plots are curves concave upwards, plots of [(VO/VM)-1]/[M] and 1/VM versus [M] are hyperbolas concave downwards and upwards respectively. Moreover plots of KM/VM against [M] are linear. However, this model does not explain some observations, under conditions of high ionic strength (gamma/2 greater than or equal to 0,1), where Dixon plots are curves concave upwards, plots of [VO/VM)-1]/[M] versus [M] strainght lines, the plot of 1/VM against [M] is a straight line or a curve concave upwards of positives slopes and the plot of KM/VM versus [M] a curve of positive slope concave upwards. These experimental data might be interpreted by an extension of the preceding model to a mechanism with two enzymatic binding sites under kinetic conditions that are determined.
[Acetylcholinesterase. II. Experimental aspects of interaction with reversible effectors under conditions of high ionic strength].
Interaction of usual effectors with acetylcholinesterase (EC 3.1.1.7) from bovine erythrocytes was examined under conditions of high ionic strength (gamma/2 greater than or equal to 0,1). Detailed kinetic investigation of the hydrolysis of acetylcholine by acetylcholinesterase in the presence of modifiers shows that the effects produced by numerous quaternary nitrogen compounds on the enzyme can be explained on the basis of binding of the effectors to the anionic subsite of the active center. The various kinetic behaviors, that are observed, are dependent on the relative values of the deacetylation rate constant ak of the complex acetylated enzyme-modifier and of the rate constant k-2 defined by : (see article) with respect to the value of the deacetylation rate constant K of the acetylated enzyme. If a identical to [1--(k/k-2)]-1, it is shown that interaction of the enzyme with tetraethylammonium, pentamethonium, hexamethonium and gallamine ions is characterized by : a greater than a and k-2 greater than k therefore, these modifiers accelerate deacetylation. On the other hand, inhibition of acetylcholinestase by methylpyridinium, d-tubocurarine, tetra-n-propylammonium, tetra-n-butylammonium, decamethonium and succinylbischoline is consistent with one of the conditions : a less than a and k-2 greater than or equal to k or a greater than a and k-2 less than k and inhibition by tetramethylammonium, phenyltrimethylammonium, 3-hydroxyphenyl-triethylammonium, N-methylacridinium and bis (3-aminopyridinium)-1,10-decane ions agrees with one of the two previous conditions or with : (see article) consequently, the effect of these ligands on the deacetylation step is undetermined. However, the effects of choline chloride, thiazinamium methyl sulfate and thioridazine hydrochloride are not entirely consistent with this mechanism but support the existence of a functional peripheral anionic site which is distinct from the anionic subsite of the active center.