Fekonja Ota, Zorec-Karlovsek Majda, El Kharbili Manale, Fournier Didier, Stojan Jure
Institute of Biochemistry, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia.
J Enzyme Inhib Med Chem. 2007 Aug;22(4):407-15. doi: 10.1080/14756360601143857.
The cholinesterases have been investigated in terms of the effects of methanol and ethanol on substrate and carbamate turnover, and on their phosphorylation. It was found: 1) that at low substrate concentrations the two alcohols inhibit all three tested cholinesterases and that the optimum activities are shifted towards higher substrate concentrations, but with a weak effect on horse butyrylcholinesterase; 2) that methanol slows down carbamoylation by eserine and does not influence decarbamoylation of vertebrate and insect acetylcholinesterase and 3) that ethanol decreases the rate of phosphorylation of vertebrate acetylcholinesterase by DFP. Our results are in line with the so-called 'approach-and-exit' hypothesis. By hindering the approach of substrate and the exit of products, methanol and ethanol decrease cholinesterase activity at low substrate concentrations and allow for the substrate inhibition only at higher substrate concentrations. Both effects appears to be a consequence of the lower ability of substrate to substitute alcohol rather than water. It also seems that during substrate turnover in the presence of alcohol the transacetylation is negligible.
针对甲醇和乙醇对底物及氨基甲酸酯周转以及它们磷酸化作用的影响，对胆碱酯酶进行了研究。结果发现：1）在低底物浓度下，这两种醇会抑制所有三种受试胆碱酯酶，且最佳活性向更高底物浓度偏移，但对马丁酰胆碱酯酶的影响较弱；2）甲醇会减缓毒扁豆碱的氨甲酰化作用，且不影响脊椎动物和昆虫乙酰胆碱酯酶的脱氨甲酰化作用；3）乙醇会降低二异丙基氟磷酸酯对脊椎动物乙酰胆碱酯酶的磷酸化速率。我们的结果符合所谓的“接近-离开”假说。通过阻碍底物的接近和产物的离开，甲醇和乙醇在低底物浓度下会降低胆碱酯酶活性，仅在较高底物浓度时才会出现底物抑制。这两种效应似乎都是由于底物替代醇而非水的能力较低所致。在有醇存在的情况下进行底物周转时，转乙酰化作用似乎也可忽略不计。
