Inhibition of acetylcholinesterase by thiamine. A structure-function study

Area of Science:

• Biochemistry
• Enzyme kinetics
• Pharmacology

Background:

• Acetylcholinesterase (AChE) is a crucial enzyme in neurotransmission.
• Thiamine (vitamin B1) and its derivatives are essential for various metabolic processes.
• Understanding enzyme inhibition mechanisms is key to drug development.

Purpose of the Study:

• To investigate the inhibitory effects of thiamine-related compounds on electric eel acetylcholinesterase.
• To determine the specific sites of inhibition on the thiamine molecule.
• To elucidate the role of molecular structure and protonation in enzyme inhibition.

Main Methods:

• Assay of 18 thiamine analogs against electric eel acetylcholinesterase.
• Ellman's method was used to measure enzyme activity at pH 7.00 and 8.25.
• Kinetic analysis using Michaelis-Menten models to determine inhibition constants (Ki).

Main Results:

• The positively charged quaternary nitrogen atom of thiamine analogs was identified as the primary inhibition site.
• Alkyl groups exhibited a secondary inhibitory role via hydrophobic interactions with the enzyme.
• Enzyme inhibition was significantly influenced by the protonation state of the thiamine derivatives.

Conclusions:

• The quaternary nitrogen is critical for acetylcholinesterase inhibition by thiamine analogs.
• Molecular structure, particularly hydrophobic regions and protonation, modulates inhibitory potency.
• Findings provide insights into the structure-activity relationships of thiamine-based enzyme inhibitors.