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 K m of 25 W WM. It is proposed that S-adenosylmethionine is the source of a 5P-deoxyadenosyl radical which initiates the rearrangement in a similar manner as it does in analogous rearrangements catalyzed by coenzyme B IPdependent enzymes. Possible roles of S-adenosylmethionine as a radical source in higher plants are discussed.z 1998 Federation of European Biochemical Societies.

Enhancing the Methyl-Donor Activity of Methylcobalamin by Covalent Attachment of DNA

“…The main fraction eluting at 7 ± 7.5% MeCN was collected and gave 5.5 mmol (63%, determined spectroscopically) of the raw cyano corrinoid 4, which was precipitated with acetone. To obtain the dipotassium salt, 4 was dissolved in a buffer (0.1m KCl, 100 mm KH 2 PO4/K 2 HPO4, pH 7), desalted by filtration through an RP18 cartridge, and precipitated from H 2 Table 2. N(3N) …”

“…± Except for higher plants [1] [2], most spheres of life make use of vitamin B 12 derivatives as vital and uniquely structured, cobalt (Co)-containing cofactors [3]. The structural features of vitamin B 12 (cyanocobalamin; 1) are the Cocoordinating corrin ligand and a 5,6-dimethyl-1H-benzimidazole (DMB) nucleotide [4] [5].…”

“…The structural features of vitamin B 12 (cyanocobalamin; 1) are the Cocoordinating corrin ligand and a 5,6-dimethyl-1H-benzimidazole (DMB) nucleotide [4] [5]. In methylcobalamin (2) and coenzyme B 12 (3), a Me or adenosyl group, respectively, is bound to the metal center [4] [6] [7], which is crucial for the biological properties of these two organometallic coenzymes [8] [9].…”

“…Here, we report on the covalent attachment of two deoxythymidylate units at the ribose moiety of the nucleotide parts of vitamin B 12 (1) and of methylcobalamin (2). We have studied the structure and altered organometallic reactivity of the resulting B 12 ÀDNA conjugates, which were isolated as the dipotassium cyano-and Mecob(III)alaminates K 2 -4 and K 2 -5, resp.…”

Ecological Arsenal and Developmental Dispatcher. The Paradigm of Secondary Metabolism

“…Plants do not produce vitamin B 12 and it has been a long-standing question what molecule takes the role of this cofactor in intramolecular migration reactions. The answer has been provided very recently by the group of János Rétey (University of Karlsruhe) who discovered that during an intramolecular migration in the biosynthesis of the anticholinergic alkaloid scopolamine in Jimson weed, 5Ј-deoxyadenosyl radical is formed from S-adenosyl-Met (11). This work has defined a new role in plants for S-adenosyl-Met, known in plant metabolism mainly as a major methyl group donor.…”