Tentoxin (cyclo(N-methyl-L-alanyl-L-leucyl-N-methyl-trans-dehydrophenyl-alanyl-glycyl)) is a natural cyclic tetrapeptide produced by phytopathogenic fungi from genus Alternaria.
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Achatin-I (glycyl-phenylalanyl-alanyl-aspartic acid) is a neuroexcitatory tetrapeptide from giant African snail (Achatina fulica).