The final step in the biosynthesis of hydrogenobyrinic acid is catalyzed by the cobH gene product with precorrin-8x as the substrate

Abstract

The final enzymatic reaction in the conversion of precorrin-6x to hydrogenobyrinic acid by cell-free protein preparations from Pseudomonas denitrificans was shown to be inhibited by hydrogenobyrinic acid. Use was made of this property to prepare the last biosynthetic precursor of hydrogenobyrinic acid, named precorrin-8x. Double-labeling experiments, mass spectrometry, and UV-visible light spectroscopy studies established that precorrin-8x was at the oxidation level of a corrin and differed from precorrin-6x by two additional methyl groups (presumably at C-5 and C-15) and decarboxylation of the acetic acid side chain at C-12. The recent isolation of precorrin-6x (24), a biosynthetic precursor of hydrogenobyrinic acid (compound 5a in Fig. 1) (8,20), and the elucidation of the structure of precorrin-6x octamethyl ester (compound 2c in Fig. 1) (22) have dramatically changed the direction of research on the biosynthesis of vitamin B12. This discovery has modified our views concerning the order of the biochemical events required for the synthesis of the corrin macrocycle and has permitted a clear proposal for the biosynthetic processes occurring during the conversion of precorrin-6x (compound 2a in Fig. 1) into hydrogenobyrinic acid. In particular, this study suggested the involvement of an NADPH-dependent reduction of precorrin-6x as the first enzymatic reaction (Fig. 2) (24). Conclusive evidence for this reduction step was recently gained when precorrin-6y (compound 3 in Fig.

Cobalt-dependent Transcriptional Switching by a Dual-effector MerR-like Protein Regulates a Cobalt-exporting Variant CPx-type ATPase

“…Unlike Synechocystis PCC 6803, many organisms do not contain the genes for vitamin B 12 biosynthesis, and such organisms have no requirement for cobalt (7). Precorrin isomerase from Pseudomonas denitrificans is known to bind avidly to its product, hydrogenobyrinic acid, which consequently co-purifies with the enzyme (8), suggesting that a domain of CoaR interacts with hydrogenobyrinic acid.…”

Biosynthesis of vitamin B12

“…CobF then becomes the prime candidate for the C-l methyl transferase catalyzing the insertion of the sixth methyl group, perhaps concerted with deacetylation at C-l to reach precorrin-6x (Scheme I). The route from precorrin-6x to (cobalt-free) hydrogenobyrinic acid (Scheme I) has recently been described at the enzyme level [5,7], so that almost every intermediate in the aerobic pathway has now been identified by NMR spectroscopy and all of the functions necessary for corrin biosynthesis assigned in I? denitrl@cans.…”

“…(-+ Factor IV, 2) [2], two further methylations at C-l 1, C-l (+ precorrin 6x, 3) [3,4] reduction at C-18, 19 (precorrin 6y, 4) [5], methylation at C-5, C-15 with decarboxylation of the C-12 acetate side chain (precorrin 8x, 5) [6] and, finally [7] [1,5] sigmatropic shift of the C-l 1 methyl to C-12 to afford the cobalt-free corrin (6) (Scheme I).…”

Biosynthesis of vitamin B12 in Pseudomonas denitrificans: the biosynthetic sequence from precorrin-6y to precorrin-8x is catalyzed by the cobL gene product

“…The first one, catalyzed by the cobK gene product, is the NADPH-dependent reduction of precorrin-6x to a dihydro derivative, called precorrin-6y (2,14). The other reaction is a rearrangement into hydrogenobyrinic acid of its isomeric ultimate precursor, named precorrin-8x (11). This reaction is catalyzed by the product of the cobH gene (11).…”

“…The enzymatic reactions involved in the conversion of precorrin-6x to hydrogenobyrinic acid have been investigated. Two of these reactions are described in the accompanying reports (2,11). The first one, catalyzed by the cobK gene product, is the NADPH-dependent reduction of precorrin-6x to a dihydro derivative, called precorrin-6y (2,14).…”