Cobamide-containing membrane protein complex in Methanobacterium

AbstractIn Methanobacterium thermoautotrophicum, most of the sole cellular cobamide, 5-hydroxybenzimidazolylcobamide (factor III [(1986) Anal. Biochem., submitted]) is bound to a membrane protein. This corrinoid protein is solubilized as a protein complex of Mr~500 000 by 5% nonpolar detergents. The complex is stable in 7 M urea. In SDS, two smaller fractions of Mr~ 30 000 and $̃60 000 carrying the cobamide are found. The unusual properties of the corrinoid enzyme complex suggest a novel function in the metabolism of CO2 and Hz in methanogens