Last revised by Daniel J Bell on 2 Aug 2021

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. 

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

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


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
    • catalyzes 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

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).

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

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

Molybdenum was discovered by Swedish chemist Carl Wilhelm Scheele (1742-1786) in 1778 7. He originally thought it was lead, thus the element was named for the Ancient Greek word molybdos, meaning "lead-like" 1.

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Cases and figures

  • Figure 1: molybdenum
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  • Figure 2: periodic table
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