Molybdenum

Molybdenum (chemical symbol Mo) is one of the essential trace elements. It complexes with a molecule called molybdopterin to form molybdenum cofactor, essential for the functioning of several important metabolic enzymes. 

Chemistry

Basic chemistry

Molybdenum has the atomic number 42, with an atomic weight of 95.94 g/mol. It is a transition metal with a silvery-white colouration ².  

Radiochemistry

35 isotopes of molybdenum are known, of these 7 are stable and 28 unstable, i.e. radioactive. Although it is thought that there may be as many as 30 isotopes still to be discovered ⁴. 

Diet, absorption, transport and storage

pending

Biological function

Molybdenum is essential for the normal functioning of four enzymes (molybdoenzymes) in humans:

• sulfite oxidase
  • oxidation of sulfite to sulfate, the terminal reaction in the oxidation of S-containing amino acids
• xanthine oxidase
  • catalyses hypoxanthine to xanthine, and xanthine to uric acid, important in the purine degradation pathway
• aldehyde oxidase
  • key for hepatic drug metabolism
• mitochondrial amidoxime-reducing component (mARC)
  • reduction of some N-hydroxylated substrates ¹

Deficiency

True molybdenum deficiency is very rare, with a few isolated case reports, mainly in those on total parenteral nutrition ³.Also see molybdenum cofactor deficiency (MCD).

Toxicity

No toxicity has been reported in humans from excessive intake of molybdenum ⁵. 

Radiological importance

• molybdenum metal is a key component of the anodes in some x-ray tubes, especially in mammography
• molybdenum generators are important as a source for Tc-99m

History and etymology

Molybdenum was discovered by Karl Scheele, a Swedish chemist, in 1778. He originally thought it was lead, thus the element was named for the Ancient Greek word molybdos, meaning "lead-like" ¹.