کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
2581767 1561646 2010 7 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Molecular basis of inhibition of substrate hydrolysis by a ligand bound to the peripheral site of acetylcholinesterase
موضوعات مرتبط
علوم زیستی و بیوفناوری علوم محیط زیست بهداشت، سم شناسی و جهش زایی
پیش نمایش صفحه اول مقاله
Molecular basis of inhibition of substrate hydrolysis by a ligand bound to the peripheral site of acetylcholinesterase
چکیده انگلیسی
Acetylcholinesterase (AChE) contains a narrow and deep active site gorge with two sites of ligand binding, an acylation site (or A-site) at the base of the gorge and a peripheral site (or P-site) near the gorge entrance. The P-site contributes to the catalytic efficiency of substrate hydrolysis by transiently binding substrates on their way to the acylation site, where a short-lived acyl enzyme intermediate is produced. Ligands that bind to the A-site invariably inhibit the hydrolysis of all AChE substrates, but ligands that bind to the P-site inhibit the hydrolysis of some substrates but not others. To clarify the basis of this difference, we focus here on second-order rate constants for substrate hydrolysis (kE), a parameter that reflects the binding of ligands only to the free form of the enzyme and not to enzyme-substrate intermediates. We first describe an inhibitor competition assay that distinguishes whether a ligand is inhibiting AChE by binding to the A-site or the P-site. We then show that the P-site-specific ligand thioflavin T inhibits the hydrolysis of the rapidly hydrolyzed substrate acetylthiocholine but fails to show any inhibition of the slowly hydrolyzed substrates ATMA (3-(acetamido)-N,N,N-trimethylanilinium) and carbachol. We derive an expression for kE that accounts for these observations by recognizing that the rate-limiting steps for these substrates differ. The rate-limiting step for the slow substrates is the general base-catalyzed acylation reaction k2, a step that is unaffected by bound thioflavin T. In contrast, the rate-limiting step for acetylthiocholine is either substrate association or substrate migration to the A-site, and these steps are blocked by bound thioflavin T.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Chemico-Biological Interactions - Volume 187, Issues 1–3, 6 September 2010, Pages 135-141
نویسندگان
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