Xanthine oxidase, the enzyme that converts purine bases into uric acid, needs molybdenum as a cofactor to function optimally. Low levels of molybdenum, which is fairly common, will compromise Xanthine oxidase activity leading to downregulation of the enzymatic clearing of purine bases from the body leading to a decreased Uric acid (<208).
Molybdenum is integral to a process called sulfoxidation, which is part of the phase II liver detoxification pathways.