Abstract
Over 50 years ago, a deadly autoimmune disease known as pernicious anemia, which is characterized by neurological and hematological abnormalities, had no known cure. The isolation of the anti-pernicious anemia factor from liver extracts by Folkers and Smith in 1948 represented a breakthrough in the treatment of this disease (21, 25). Named vitamin B12, this compound could be isolated as pure, red crystals from various animal and microbial sources, and the X-ray crystal structure of this complex molecule, one of the largest nonpolymeric natural compounds, was determined in the 1950s by Dorothy Hodgkin et al. (Fig. (Fig.1A)1A) (8). Since that time, thousands of researchers have identified and characterized a variety of enzymes that utilize B12 cofactors, determined the complex pathway for B12 absorption in humans, and elucidated the microbial pathways for B12 biosynthesis. Other forms of vitamin B12 have been found in nature, but their functions are not fully understood. In this issue of the Journal of Bacteriology, Anderson et al. provide evidence that a form of B12 known as “pseudo-B12” (Fig. (Fig.1B)1B) is a physiologically important form of B12 in Salmonella enterica serovar Typhimurium (1). FIG. 1. Corrinoids produced by S. enterica. Cobalamin (A) and pseudo-B12 (B) differ in their α-axial ligands. The β-axial ligand (R) is 5′-deoxyadenosine or -CH3 in B12 cofactors and -CN in vitamin B12. Collectively, these molecules are ... Unlike all other vitamins, vitamin B12 is not produced by plants; rather, its biosynthesis is restricted to certain prokaryotes (23). Animals obtain B12 from food or, in some cases, directly from resident B12-producing microbes (28). S. enterica has long been used as a model organism for studying B12 biosynthesis (23).
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