Cobamide‐containing membrane protein complex in <i>Methanobacterium</i>

Abstract

In 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 M r ~500 000 by 5% nonpolar detergents. The complex is stable in 7 M urea. In SDS, two smaller fractions of M r ~ 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 CO 2 and Hz in methanogens.