Characterization of polyneuridine aldehyde esterase, a key enzyme in the biosynthesis of sarpagine/ajmaline type alkaloids.

Polyneuridine aldehyde esterase (PNA-esterase) was isolated and partially purified from cell suspension cultures of RAUWOLFIA SERPENTINA B ENTH. The exceptionally high substrate specific enzyme catalyses the conversion of the monoterpenoid C (10-) into the C (9-)unit at the stage of polyneuridine aldehyde during the biosynthesis of sarpagine/ajmaline type alkaloids. The enzymatically formed compound is the new, labile indole alkaloid 16-epivellosimine. It is this alkaloid which functions as a branch point of the biogenetic routes leading to sarpagan and ajmalan type alkaloids. PNA-esterase occupies a key position in the biosynthesis of both alkaloid groups.