Question

whats the mode of action for organophostphate insectisides and carbomates.

please include the reaction for both thanks

Answer 1

• Mode of action of organophosphate pesticide: Organophosphates are agricultural insecticides. These agents inhibit the enzyme acetylcholinesterase, which is responsible for the degradation of acetylcholine. The organophosphate binds to the enzyme, causing it to undergo a conformational change at its binding site to acetylcholine. Once AChE has been inactivated, ACh accumulates throughout the nervous system, resulting in overstimulation of muscarinic and nicotinic receptors.

• Mode of action of carbamate: toxicity due to inhibition of acetylcholinesterases - however unlike the organophosphates they do not need to be modified ( S --> O ) before becoming effective.
• They do not penetrate the CNS so most effects are respiratory in nature.Depression of respiration combined with pulmonary edema is the usual cause of death from poisoning by N-methyl carbamate compounds.
• The N-methyl carbamate esters cause reversible carbamylation of acetylcholinesterase enzyme, allowing accumulation of acetylcholine, the neuromediator substance, at parasympathetic neuroeffector junctions (muscarinic effects), at skeletal muscle myoneural junctions and autonomic ganglia (nicotinic effects), and in the brain (CNS effects).
• The carbamyl-acetylcholinesterase combination dissociates more readily than the phosphoryl-acetylcholinesterase complex produced by organo-phosphate compounds. This liability has several important consequences:

  

  • 1) it tends to limit the duration of N-methyl carbamate poisonings,
  • 2) it accounts for the greater span between symptom-producing and lethal doses than exists in the case of most organophosphate compounds, and
  • 3) it frequently invalidates the measurement of blood cholinesterase activity as a diagnostic index of poisoning as it disassociates rapidly enough not to be detectable...although toxicity had occured earlier with exposure....

Some carbamates are quite toxic. others less so. Carbaryl has low toxicity for mammals though Perimicarb is highly toxic to mammals but not readily absorbed through the skin.