A protein complex consisting of three polypeptides which also contains molybdenum, a molybdopterin guanine dinucleotide and iron-sulfur clusters. This protein complex catalyzes the reversible conversion of CO2 and methanofuran to formylmethanofuran during methanogenesis. [ http://www.ncbi.nlm.nih.gov/pubmed/1915887 GOC:mengo_curators http://www.ncbi.nlm.nih.gov/pubmed/8954165 ]