Abstract
The Co‐methyl and the Co‐aquo derivative of 5‐hydroxybenzimidazolylcobamide (factor III) were isolated as the major natural corrinoids from Methanosarcina barkeri ‘Fusaro’. They were characterized by their UV/VIS‐spectra, their chromatographic behaviour, and their electrophoretic properties. The portion of Co‐methyl‐factor III was found to be 70–80% whereas Co‐aquo‐factor III contributed 20–30% to the total amount of corrinoids.