Molybdenum in Biology - An Essential Trace Element
Molybdenum and enzymes
Molybdenum is an essential constituent of enzymes involved in animal and plant metabolism.
The enzyme xanthine oxidase oxidizes hypoxanthine to xanthine and xanthine to uric acid in purine catabolism. Cofactor deficiency leads to abnormal sulfur and xanthine metabolism, i.e., high and low cystine and uric acid concentrations in plasma and urine. Sulfite oxidase catalyzes the oxidation of sulfite to sulfate, and aldehyde oxidase catalyzes the oxidation of aldehydes and various nitrogen-containing aromatic heterocyclic compounds.
Van Gennip, A. H., Abeling, N. G., Stroomer, A. E. M., Overmars, H. and Bakker, H. D., J. Inherit. Metab. Dis. , 1994, 17, 142.
Three Mo-enzymes have been found in plants. Nitrate reductase catalyses the reduction of nitrate, the key step in inorganic nitrogen assimilation. Aldehyde oxidase catalyzes the last step in the biosynthesis of the phytohormones indole acetic acid and abscisic acid. Xanthine dehydrogenase is involved in purine catabolism.
With the exception of bacterial nitrogenase, Mo-enzymes share a similar pterin at their catalytic sites, the molybdenum cofactor. Molybdenum is biologically inactive unless it is complexed by the cofactor. The core structure of molybdopterin is conserved in all organisms.