engleski

Inhibition of human serum butyrylcholinesterase phenotypes by ethopropazine

Ethopropazine is a selective inhibitor (to a high degree a specific inhibitor) of butyrylcholinesterase (BChE ; EC 3.1.1.8) and is used to differentiate BChE from acetylcholinesterase (AChE ; EC 3.1.1.7) in whole blood or other tissues where both AChE and BChE are present. Ethopropazine, having a quaternary nitrogen, is expected to be a better inhibitor of the usual human serum BChE than the atypical enzyme or its heterozygotes. We have measured the activity of human sera with 0.5 and 1.0 mM acetylthiocholine as substrate in the presence and in the absence of 20 uM ethopropazine in 0.1 M phosphate buffer, pH=7.4 at 37 oC with the DTNB reagent (Ellman et al. 1961). The sera were from individuals who had different BChE homozygous and heterozygous phenotypes of usual (U), atypical (A), fluoride-resistant (F), Kalow (K), J, or silent (S) variants. Three to five sera of each BChE phenotype were tested. In our experimental conditions, the activities of UU, UA, FF/FS, AF, AJ/AK, AA/AS sera were inhibited 98, 94, 92, 87, 85 and 74%, respectively. The contribution of partially uninhibited BChE activity might affect the estimate of AChE activity in whole blood or other tissues. Furthermore, the AChE activity of human erythrocytes is 8% inhibited by 20 uM ethopropazine which should also be taken into account when applying ethopropazine for the differentiation of AChE and BChE activities in whole blood.

ethopropazin; acethylcholinesterase; butyrylcholinesterase; phenotypes

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