Department of Bacteriology, University of Wisconsin, Madison, Wisconsin 53726-1521, USA.
J Biol Chem. 2010 Jan 29;285(5):2911-7. doi: 10.1074/jbc.M109.059485. Epub 2009 Nov 21.
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 Co(2+)Cbl bound in the active site of PduO-type ATP-dependent corrinoid adenosyltransferase enzymes. Free dihydroflavins (dihydroriboflavin, FMNH(2), and FADH(2)) effectively drove the adenosylation of Co(2+)Cbl by the human and bacterial PduO-type enzymes at very low concentrations (1 microm). These data show that adenosyltransferase enzymes lower the thermodynamic barrier of the Co(2+) --> 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.
将钴胺素转化为其生物活性形式腺苷钴胺素所需的生物还原剂的来源一直难以捉摸。在这里，我们表明游离或结合在蛋白质上的二氢黄素可以作为 PduO 型 ATP 依赖性钴胺素腺苷转移酶结合在活性位点的 Co(2+)Cbl 的还原剂。游离二氢黄素（二氢核黄素、FMNH(2) 和 FADH(2)) 在非常低的浓度（1 微摩尔）下有效地驱动了人和细菌 PduO 型酶的 Co(2+)Cbl 的腺苷化。这些数据表明，腺苷转移酶降低了 Co(2+) --> Co(+)还原的热力学障碍，这是形成腺苷钴胺素独特的有机金属 Co-C 键所必需的。总的来说，我们的体内和体外数据表明，迄今为止鉴定的钴胺素还原酶很可能是电子转移蛋白，而不是酶。
