Enzyme degradation

Most enzymes are included in the catabolism of both classical and peptide transmitters and pharmacological inhibition of most of these can have consequences for synaptic transmission. Though, only in a couple of situation the enzyme-catalyzed degradation is significant in the physiological inactivation of transmitter. The Acetylcholine is hydrolyzed by:-

Acetylcholinesterase (AChE) that cleaves the transmitter molecule into choline and acetate. The Choline is taken back into the presynaptic nerve terminal by a Na+-dependent transporter. The AChE has a very high catalytic activity and at the neuromuscular junction can decrease the concentration of ACh from about 1 mM instantly after release to virtually zero in about 1 ms.

Adenosine 5¢-triphosphate (ATP), the cotransmitter at several synapses, is the only other transmitter inactivated at the synapse by the enzyme-catalyzed degradation.