Trans-4-aminocrotonic acid

C/s-4-aminocrotonic acid, an analogue of the central neurotransmitter GABA, has the folded conformation (13.26) and is biologically inactive, whereas the trans isomer (13.23) acts as efficiently as GABA in the mammalian central nervous system. This shows that the extended, rather than the folded, conformation of GABA is the important one in neurotransmission (Johnston et al.y 1975). 

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