Molybdenum is an essential trace mineral in animal and human nutrition. It is found in several tissues of the human body and is required for the activity of some enzymes that are involved in catabolism, including the catabolism of purines and the sulfur amino acids. Molybdenum is a transition metal with atomic number 42 and an atomic weight of 95.94 daltons. Its symbol is Mo. Compounds of molybdenum are among the scarcer constituents of the earth's crust. In fact, molybdenum is only about three times more abundant than gold. The principal ore of molybdenum is molybdenite (molybdenum disulfide). Organic forms of molybdenum are found in living matter, from bacteria to animals, including humans.
In spite of its low abundance, molybdenum deficiency in humans is rare but it has been described. A patient on long-term total parenteral nutrition (TPN) developed a syndrome characterized by hypouricemia, hypermethioninemia, low urinary sulfate excretion, tachycardia, tachypnea and mental and visual disturbances. The syndrome worsened with the administration of L-methionine and the patient eventually became comatose. The patient improved when molybdenum, in the form of ammonium molybdate, was added to the TPN. The deleterious effects of molybdenum deficiency were primarily due to the accumulation of sulfite coming from the catabolism of L-cysteine. Sulfite is toxic to the nervous system and molybdenum is necessary for its metabolism to a nontoxic form.
Animals can be made molybdenum deficient by feeding them diets containing high amounts of tungsten or copper. Both tungsten and copper are molybdenum antagonists. Molybdenum deficiency has also been produced experimentally in goats by feeding them purified diets, very low in molybdenum. Molybdenum deficiency in animals results in retarded weight gain, decreased food consumption, impaired reproduction and a shortened life expectancy.
High intake of molybdenum is antagonistic to copper and can produce a condition in animals known as molybdenosis. Molybdenum-containing compounds, such as tetrathiomolybdate are currently in clinical trials for the treatment of metastatic cancer and Wilson disease. The use of copper antagonistic substances in these disorders, is known as copper depletion therapy.
