The classification of esterases which hydrolyse organophosphates: recent developments

Area of Science:

• Biochemistry
• Enzymology
• Chemical Biology

Background:

• The 1984 IUB classification grouped paraoxon-hydrolyzing enzymes with arylesterases (EC 3.1.1.2).
• Discoveries revealed some paraoxonases do not hydrolyze phenylacetate, necessitating a new classification.
• The 1989 revision introduced Aryldialkylphosphatase (EC 3.1.8.1) under phosphoric triester hydrolases (EC 3.1.8).

Purpose of the Study:

• To address the evolving classification of enzymes involved in organophosphorous compound hydrolysis.
• To differentiate between arylesterases and aryldialkylphosphatases based on substrate specificity.
• To propose revisions for enzymes hydrolyzing organophosphorous diesters, such as nerve agents.

Main Methods:

• Review of existing enzyme classification systems (IUB 1984, 1989).
• Analysis of substrate specificity data for paraoxonases and arylesterases.
• Examination of evidence for enzymes hydrolyzing P-F and P-CN bonds in organophosphorous diesters.

Main Results:

• Some enzymes hydrolyzing phenylacetate do not hydrolyze paraoxon, and vice versa, highlighting classification complexities.
• Evidence suggests enzymes hydrolyzing organophosphorous diesters (e.g., tabun, soman) function as organophosphorous acid anhydrolases.
• A proposed deletion of EC 3.8.2.1 and introduction of diisoprophylfluorophosphatase (EC 3.1.8.2) is suggested.

Conclusions:

• The classification of organophosphorous hydrolases requires ongoing refinement.
• Enzyme substrate specificity and cofactor requirements present significant challenges for accurate classification and nomenclature.
• Further research is needed to fully characterize and classify enzymes with diverse organophosphorous substrate specificities.