Biosynthesis of vitamin B12: isolation of precorrin-6x, a metal-free precursor of the corrin macrocycle retaining five S-adenosylmethionine-derived peripheral methyl groups.
delta-Aminolevulinic acid and trimethylisobacteriochlorin are converted by cell-free protein preparations from Pseudomonas denitrificans into a metal-free pigment, precorrin-6x. This pigment, which accumulates when the cell-free system lacks NADPH, can be enzymically converted in high yield (greater than 50%) into hydrogenobyrinic acid by the complete enzyme preparation. Double-labeling experiments establish that precorrin-6x carries five C-methyl groups, which appear at C-1, C-2, C-7, C-12 alpha, and C-17 of the hydrogenobyrinic acid formed enzymically from precorrin-6x. This precursor of the corrin macrocycle is at the dehydrocorrin level of oxidation, has undergone ring contraction and extrusion of C-20, but still carries the acetic acid side chain at C-12. It is demonstrated that the conversion of precorrin-6x into hydrogenobyrinic acid specifically requires an NADPH-dependent reduction step.
Thibaut
D
D
Département de Chimie Analytique, Centre de Recherche de Vitry, Rhône-Poulenc Santé, Vitry-sur-Seine, France.
Debussche
L
L
Blanche
F
F
D009682:Magnetic Resonance Spectroscopy; D008745:Methylation; D009249:NADP / Q000378:metabolism; D011549:Pseudomonas / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000378:metabolism; D014578:Uroporphyrins / Q000302:isolation & purification* / Q000378:metabolism; D014805:Vitamin B 12 / Q000096:biosynthesis* / Q000737:chemistry
D014578:Uroporphyrins; C066509:precorrin 6x; D009249:NADP; D012436:S-Adenosylmethionine; D014805:Vitamin B 12