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Biochem Biophys Res Commun. 2017 Aug 5;489(4):451-454. doi: 10.1016/j.bbrc.2017.05.168. Epub 2017 May 29.

On the use of the experimentally determined enzyme inhibition constant as a measure of absolute binding affinity.

Author information

1
Computer-Aided Molecular Design Laboratory, Mayo Clinic, Rochester, MN 55905, USA.
2
Computer-Aided Molecular Design Laboratory, Mayo Clinic, Rochester, MN 55905, USA. Electronic address: pang@mayo.edu.

Abstract

Defined as a state function representing an inhibitor's absolute affinity for its target enzyme, the experimentally determined enzyme inhibition constant (Ki) is widely used to rank order binding affinities of different inhibitors for a common enzyme or different enzymes for a common inhibitor and to benchmark computational approaches to predicting binding affinity. Herein, we report that adsorption of bis(7)-tacrine to the glass container surface increased its Ki against Electrophorus electricus acetylcholinesterase (eeAChE) to 3.2 ± 0.1 nM (n = 5) compared to 2.9 ± 0.4 pM (n = 5) that was determined using plastic containers with other assay conditions kept the same. We also report that, due to binding or "adsorption" of bis(7)-tacrine to the inactive eeAChE, the bis(7)-tacrine Ki increased from 2.9 ± 0.4 pM (n = 5) to 734 ± 70 pM (n = 5) as the specific eeAChE activity decreased from 342 U/mg to 26 U/mg while other assay conditions were kept the same. These results caution against using Kis to rank order binding potencies, define selectivity, or benchmark computational methods without knowing detailed assay conditions.

KEYWORDS:

Adsorption; Affinity; Dissociation constant; Inhibition constant; Nonspecific binding; Nontarget site binding

PMID:
28571743
DOI:
10.1016/j.bbrc.2017.05.168
[Indexed for MEDLINE]
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