Confusion arises from the different meanings of the term "disulfide". Molybdenum disulfide (MoS) consists of separated sulfide centers, in association with molybdenum in the formal +4 oxidation state (that is, Mo and two S). Iron disulfide (pyrite, FeS) on the other hand consists of , or S–S dianion, in association with divalent iron in the formal +2 oxidation state (ferrous ion: Fe). Dimethyldisulfide has the chemical binding CH–S–S–CH, whereas carbon disulfide has no S–S bond, being S=C=S (linear molecule analog to CO). Most often in sulfur chemistry and in biochemistry, the disulfide term is commonly ascribed to the sulfur analogue of the peroxide –O–O– bond. The disulfide bond (–S–S–) plays a major role in the conformation of proteins and in the catalytic activity of enzymes.