The role and source of 5'-deoxyadenosyl radical in a carbon skeleton rearrangement catalyzed by a plant enzyme.

ABSTRACT

The last step in the biosynthesis of tropane alkaloids is the carbon skeleton rearrangement of littorine to hyoscyamine. The reaction is catalyzed by a cell-free extract prepared from cultured hairy roots of Datura stramonium. Adenosylmethionine stimulated the rearrangement 10-20-fold and showed saturation kinetics with an apparent Km of 25 microM. It is proposed that S-adenosylmethionine is the source of a 5'-deoxyadenosyl radical which initiates the rearrangement in a similar manner as it does in analogous rearrangements catalyzed by coenzyme B12-dependent enzymes. Possible roles of S-adenosylmethionine as a radical source in higher plants are discussed.