A small molybdenum-containing unit, known as Moco, acts as a cofactor
for oxomolybdoenzymes such as sulfite oxidase, nitrate reductase, xant
hine dehydrogenase, and dimethyl sulfoxide reductase. This review surv
eys structural, spectroscopic, and synthetic studies aimed at the eluc
idation of the structure and mechanism of action of the cofactor.