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R Arnaud

Publications and source records attributed to R Arnaud.

34 records · Page 2Linked to original sources
PubMedDate not supplied

Electron spin resonance of eumelanin from hair: photoinduced radicals in solid matrix.

KBr matrices appear to be convenient media to reveal the radicals formed on light exposure of eumelanin dispersions. The ESR signal of eumelanin dispersed at low concentration in KBr pellets is analyzed during and after irradiation at various wavelengths. Different types of radicals are observed. R'1- and R1-types of radicals are assigned, respectively, to neutral and deprotonated intrinsic phenoxy radicals of eumelanin. R'1 can be oxidized by oxygen as opposite to R1. R2- and R'2-types are formed in the indolic site. Water favours the conversion of R2, unreactive with oxygen, into R'2 which can be oxidized. R'1 and R2 result of an electron photoejection, respectively, from the phenolic and the indolic site. The R3-type radicals are associated with the band-to-band excitation of eumelanin considered as a semiorganized solid.

Electron Spin Resonance Spectroscopy↗
PubMedDate not supplied

[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.

Acetylcholinesterase↗