ID   5.5.1.36
DE   hapalindole U synthase.
CA   3-geranyl-3-[(Z)-2-isocyanoethenyl]-1H-indole = hapalindole U.
CC   -!- Requires Ca(2+).
CC   -!- The enzyme, which belongs to the Stig cyclases, has been
CC       characterized from multiple species of the cyanobacterial genera
CC       Fischerella and Westiellopsis.
CC   -!- Stig cyclases catalyze a three step process including a Cope
CC       rearrangement, 6-exo-trig cyclization and electrophilic aromatic
CC       substitution.
CC   -!- The enzyme is a heterodimer of two different proteins (AmbU1 and
CC       AmbU4). On their own, AmbU1 catalyzes a different reaction, producing
CC       12-epi-hapalindole U (cf. EC 5.5.1.32) while AmbU4 appears to be
CC       inactive.
CC   -!- Formation of hapalindole U leads to the biosynthesis of additional
CC       terpenoid indole alkaloids such as hapalindole G, ambiguine H,
CC       and ambiguine A.
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