Mo-molybdopterin cofactor (Moco) biosynthesis begins in the mitochondrial matrix with the production of cyclic pyranopterin phosphate (cPMP). Following its transport into the cytosol, cPMP is converted into molybdopterin by the molybdopterin synthase complex. The molybdenum (Mo) atom is then inserted forming the Mo-molybdopterin cofactor (active Moco). Moco can be incorporated as such into proteins or it can be further modified by sulfation prior to its insertion into proteins. (Adapted from FBrf0238243.)