Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 285, Issue 5, Pages -Publisher
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M109.059485
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Funding
- National Institutes of Health Grant [GM40313]
- Predoctoral National Research Service [F31-GM081979]
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The identity of the source of the biological reductant needed to convert cobalamin to its biologically active form adenosylcobalamin has remained elusive. Here we show that free or protein-bound dihydroflavins can serve as the reductant of Co2+ Cbl bound in the active site of PduO-type ATP-dependent corrinoid adenosyltransferase enzymes. Free dihydroflavins (dihydroriboflavin, FMNH2, and FADH(2)) effectively drove the adenosylation of Co2+ Cbl by the human and bacterial PduO-type enzymes at very low concentrations (1 mu M). These data show that adenosyltransferase enzymes lower the thermodynamic barrier of the Co2+ -> Co+ reduction needed for the formation of the unique organometalic Co-C bond of adenosylcobalamin. Collectively, our in vivo and in vitro data suggest that cobalamin reductases identified thus far are most likely electron transfer proteins, not enzymes.
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