cobamamide and propionic-acid

The Escherichia coli genome encodes seven paralogues of the crotonase (enoyl CoA hydratase) superfamily. Four of these have unknown or uncertain functions; their existence was unknown prior to the completion of the E. coli genome sequencing project. The gene encoding one of these, YgfG, is located in a four-gene operon that encodes homologues of methylmalonyl CoA mutases (Sbm) and acyl CoA transferases (YgfH) as well as a putative protein kinase (YgfD/ArgK). We have determined that YgfG is methylmalonyl CoA decarboxylase, YgfH is propionyl CoA:succinate CoA transferase, and Sbm is methylmalonyl CoA mutase. These reactions are sufficient to form a metabolic cycle by which E. coli can catalyze the decarboxylation of succinate to propionate, although the metabolic context of this cycle is unknown. The identification of YgfG as methylmalonyl CoA decarboxylase expands the range of reactions catalyzed by members of the crotonase superfamily.

Topics: Amino Acid Sequence; Carboxy-Lyases; Catalysis; Cloning, Molecular; Cobamides; Coenzyme A-Transferases; Enoyl-CoA Hydratase; Escherichia coli; Genes, Bacterial; Genome, Bacterial; Kinetics; Methylmalonyl-CoA Decarboxylase; Methylmalonyl-CoA Mutase; Molecular Sequence Data; Multigene Family; Operon; Propionates; Protein Kinases; Racemases and Epimerases; Sequence Alignment; Sequence Homology, Amino Acid; Succinic Acid

Prenatal diagnosis for combined methylmalonic aciduria and homocystinuria was performed in five at-risk pregnancies by determination of methylmalonic acid (MMA) and total homocysteine (Hcy) in amniotic fluid supernatant. The incorporation rate of [14C] propionate (+/- OHCbl) and the synthesis of cobalamin derivatives in cultured amniocytes were investigated as well as the [14C] MTHF incorporation rate in intact chorion biopsy. Our experience showed that total Hcy and MMA were clearly elevated in amniotic fluid of affected fetuses. Both the study of [14C] propionate incorporation and that of cobalamin synthesis in cultured amniocytes are useful to confirm the results of metabolite determination. The incorporation of [14C] MTHF in intact chorion biopsy seems not to be a reliable diagnostic method.

Topics: Amino Acid Metabolism, Inborn Errors; Amniocentesis; Amniotic Fluid; Cells, Cultured; Chorion; Chorionic Villi Sampling; Cobamides; Female; Gestational Age; Homocysteine; Homocystinuria; Humans; Male; Methylmalonic Acid; Pregnancy; Propionates; Tetrahydrofolates; Vitamin B 12