Biosynthesis of vitamin B12: structure of precorrin-6x octamethyl ester.
13C-labeled precorrin-6x is biosynthesized by cell-free protein preparations from Pseudomonas denitrificans in separate experiments using delta-amino[5-13C]levulinic acid and the corresponding delta-amino[4-13C]- and delta-amino[3-13C]levulinic acid-labeled forms in conjunction with S-[methyl-13C]adenosylmethionine for the latter two experiments. These labeled precorrin-6x samples, as their octamethyl esters, are studied by a range of NMR techniques. In addition, nuclear Overhauser effect difference measurements are made on unlabeled precorrin-6x ester to determine connectivities. The structure 6a so established for precorrin-6x ester (i) confirms the results reported in the preceding paper that precorrin-6x has a ring-contracted macrocycle, still carries the C-12 acetate residue, and stands at the oxidation level of a dehydrocorrin; (ii) reveals the unexpected methylation at C-11 not C-12, leading to a structure with separated chromophores; and (iii) implies that methyl migration from C-11 to C-12 occurs when precorrin-6x is converted into hydrogenobyrinic acid. Proposals for the biosynthesis of the corrin macrocycle of hydrogenobyrinic acid and vitamin B12 are made.
Thibaut
D
D
Département de Chimie Analytique, Centre de Recherche de Vitry, Rhône-Poulenc Santé, Vitry-sur-Seine, France.
Blanche
F
F
Debussche
L
L
Leeper
F J
FJ
Battersby
A R
AR
D002474:Cell-Free System; D004952:Esters; D009682:Magnetic Resonance Spectroscopy; D008745:Methylation; D015394:Molecular Structure; D011549:Pseudomonas / Q000378:metabolism; D014578:Uroporphyrins / Q000737:chemistry*; D014805:Vitamin B 12 / Q000096:biosynthesis*
D004952:Esters; D014578:Uroporphyrins; C066510:precorrin 6x octamethyl ester; D014805:Vitamin B 12