It is a member of the prymnesins, a class of hemolytic phycotoxins made by the alga Prymnesium parvum.

[1][2] It is known to be toxic to fish, causing mass fish deaths around the world, including in Texas and England, or in 2022 in the border region of Germany and Poland (Oder).

Prymnesin-1 is formed of a large polyether polycyclic core with several conjugate double and triple bonds, chlorine and nitrogen heteroatoms and O-linked sugar moieties including α-D-ribofuranose, α-L-arabinopyranose, and β-D-galactofuranose, unlike the single linked α-L-xylofuranose of prymnesin-2.

The backbone of A-type prymnesins like prymnesin-1 is reportedly made by giant polyketide synthase enzymes dubbed the "PKZILLAs".

[5] PKZILLA-1 and PKZILLA-2 have been identified with the first consisting of 45,212 amino acids making it the largest known protein.