Abstract：
:Catalysed hydrolysis of butyrylthiocholine (BTCh) by the usual (UU), fluoride-resistant (FS), AK, AJ and atypical (AA) human serum butyrylcholinesterase (EC 3.1.1.8) variants was measured in phosphate buffer pH 7.4 at 25 degrees C. pS-curves for all phenotypes were S-shaped; the activities rose to a plateau with increasing substrate concentration except at 100 mM where there was a small decrease. To obtain the catalytic constants, three equations were applied: Michaelis-Menten equation (Eq. 1), Hill equation (Eq. 2) and an equation which assumes simultaneous binding of the substrate to the catalytic site and to a peripheral site on the enzyme (Eq. 3). Over a range from 0.01 to 50 mM BTCh, the activity versus substrate concentration relationship deviated from Michaelis-Menten kinetics (Eq. 1) while data fitted well with Eqs. 2 and 3. The Michaelis-Menten equation was applied separately to two BTCh concentration ranges: the corresponding Km constants for the UU, FS, AK, AJ and AA phenotypes ranged from 0.1 to 0.2 mM (at 0.01-1.0 mM BTCh) and from 0.3 to 2.0 mM (at 1.0-50 mM BTCh). Hill coefficients (nH) calculated from Eq. 2 were similar for all phenotypes (nH approximately 0.5). The dissociation constants K1 and K2 calculated from Eq. 3 for two sites on the enzyme fell between 0.02 and 0.12 mM (K1) and 0.89 and 4.9 mM (K2) for the five phenotypes. Experimental data support the assumption that the phenotypes studied have two substrate binding sites.
journal_name
Chem Biol Interactjournal_title
Chemico-biological interactionsauthors
Simeon-Rudolf V,Reiner E,Evans RT,George PM,Potter HCdoi
10.1016/s0009-2797(99)00025-3subject
Has Abstractpub_date
1999-05-14 00:00:00pages
165-71eissn
0009-2797issn
1872-7786pii
S0009-2797(99)00025-3journal_volume
119-120pub_type
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journal_title：Chemico-biological interactions
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journal_title：Chemico-biological interactions
pub_type： 杂志文章,评审
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journal_title：Chemico-biological interactions
pub_type： 杂志文章
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journal_title：Chemico-biological interactions
pub_type： 杂志文章
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更新日期：2006-08-25 00:00:00
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journal_title：Chemico-biological interactions
pub_type： 杂志文章
doi：10.1016/0009-2797(88)90093-2
更新日期：1988-01-01 00:00:00
