Stereochemistry of the Methyl Group in (R)-3-Methylitaconate Derived by Rearrangement of 2-Methylideneglutarate Catalysed by a Coenzyme B12-Dependent Mutase
✍ Scribed by Daniele Ciceri; Antonio J. Pierik; Günter Hartrampf; Gerd Bröker; Giovanna Speranza; Wolfgang Buckel; Sir John Cornforth; Bernard T. Golding
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- German
- Weight
- 190 KB
- Volume
- 83
- Category
- Article
- ISSN
- 0018-019X
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✦ Synopsis
Dedicated to Professor Albert Eschenmoser on the occasion of his 75th birthday 2-Methylideneglutarate mutase is an adenosylcobalamin (coenzyme B 12 )-dependent enzyme that catalyses the equilibration of 2-methylideneglutarate with (R)-3-methylitaconate. This reaction is believed to occur via protein-bound free radicals derived from substrate and product. The stereochemistry of the formation of the methyl group of 3-methylitaconate has been probed using a chiral methyl group. The methyl group in 3-([ 2 H 1 , 3 H]methyl)itaconate derived from either (R)-or (S)-2-methylidene[3-2 H 1 ,3-3 H 1 ]glutarate was a 50 : 50 mixture of (R)-and (S)-forms. It is concluded that the barrier to rotation about the CÀC bond between the methylene radical centre and adjacent C-atom in the product-related radical [ . CH 2 CH( À O 2 CCCH 2 )CO 2 À ] is relatively low, and that the interaction of the radical with cob(II)alamin is minimal. Hence, cob(II)alamin is a spectator of the molecular rearrangement of the substrate radical to product radical.