engleski

Kinetics of inhibition of human serum butyrylcholinesterase (EC 3.1.1.8) heterozygous phenotypes by the dimethylcarbamate Ro 02-0683

The time course of inhibition by the dimethylcarbamate Ro 02-0683 of sera heterozygous for butyrylcholinesterase phenotyped by the inhibitor numbers as UA, UF, AF, AK or AJ, was followed from zero to 120 min by measuring the remaining activity using propionylthiocholine as substrate. The aim was to determine the rate constants of inhibition of heterozygous enzyme and of each variant as well as its contribution to the total activity. The reaction does not follow first order kinetics and it can be explained by the presence of two enzyme variants in heterozygous sera which are inhibited to different extents. The remaining activities ( y / %) vs. time (t) were fitted to the bi-exponential equation y = Q exp (-kQ t) + Z exp (-kz t) where Q and Z are activity contributions of the U, F, A, K or J variants to the total activity of the heterozygous serum and kQ and kz the respective first order rate constants of inhibition. The time course of inhibition for sera of UU, UK and UJ phenotypes is similar. This substantiates the earlier ifindings that K and J mutations lead to quantitative changes in the concentration of usual enzyme in contrast to the qualitative changes of the atypical and fluoride resistant variants. The second order rate constants of inhibition by Ro 02-0683 were calculated from the time course of inhibition of the sera variants. Contributions of the atypical variant to the total activity of UA, AK, AJ and AF heterozygous sera were 18, 28, 43 and 41 % respectively. The difference between the Ro 02-0683 inhibitor numbers for UA, AK and AJ heterozygots is the result of the different contribution of U, K or J variant to the total activity of atypical heterozygots.

atypical variant; butyrylcholinesterase; human serum cholinesterase

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