The toxic effect of the organophosphorus insecticides is due to their interference in the transfer of nerve impulses from one nerve cell to the next. When a nerve impulse reaches the end of a nerve cell, it triggers the release of a minute amount of the compound acetylcholine:

(CH^NC^C^OCCH chollnesterase - (CH3)3NCH3CH2OH + CH3CO2H (8-66)

Acetylcholine Choline Acetic acld

The acetylcholine activates a receptor on an adjacent nerve cell, causing it to carry the impulse to the next nerve cell. The acetylcholine is then hydrolyzed to choline and acetic acid by the enzyme cholinesterase as in reaction (8-66). Other enzymes then convert the choline and acetic acid back to acetylcholine on the nerve endings.

The organophosphorous pesticides bind chemically to the cholinesterase so that it can no longer catalyze the hydrolysis of acetylcholine. The resulting excess of acetylcholine hyperstimulates nerves and produces convulsions, irregular heartbeat, and choking in vertebrates.

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