IDENTIFICATION OF THE MOLYBDENUM COFACTOR OF DIMETHYL-SULFOXIDE REDUCTASE FROM RHODOBACTER-SPHAEROIDES F-SP DENITRIFICANS AS BIS(MOLYBDOPTERIN-GUANINE-DINUCLEOTIDE)MOLYBDENUM

Chemical analysis of dimethyl sulfoxide reductase from Rhodobacter sph aeroides f. sp. denitrificans has shown that its molybdenum center con tains two molybdopterin guanine dinucleotide molecules and a single at om of molybdenum. The enzyme, which exists as a monomer of 86 kDa, was shown to contain 1 mol of molybdenum, 4 mol of organic phosphate, and 2 mol of guanine per mole of protein. In addition, the relative yield of Form A, a fluorescent derivative of molybdopterin, was twice that obtained from sulfite oxidase, a protein which contains a single molyb dopterin per molybdenum. These findings correlate with the recent repo rt of the presence of two molybdopterin ligands in the tungsten cofact or of aldehyde ferredoxin oxidoreductase from Pyrococcus furiosus, pro viding the first example of a bis(pterin)molybdenum cofactor and exten ding this structural motif to the molybdopterin dinucleotide enzymes. (C) 1996 Academic Press, Inc.