As a trace element molybdenum occurs in plants and animals in concentrations of a few parts per million. Molybdenum is an essential constituent of certain enzymes that catalyse redox reactions: in plants, reduction of molecular nitrogen and nitrate; in animals, oxidation (hydroxylation) of xanthine and other purines and aldehydes. Molybdenum is capable of forming complexes with many compounds of biological importance: carbohydrates, amino acids, flavins, porphyrins; but is probably taken up, transported, and excreted in animals as the simple molybdate ion, [MoO4]2-. Molybdenum is essential for plant growth because of its involvement in the processes of nitrogen fixation and nitrate reduction. For satisfactory plant growth, some soils that are deficient in molybdenum require supplemental molybdenum.
In some animals, an essential stage in the catabolism of purines is the oxidation of xanthine to uric acid, a reaction catalysed by the molybdenum-containing enzyme xanthine oxidase. At low molybdenum concentrations, the activity of xanthine oxidase is proportional to the molybdenum concentration; but at higher concentrations, molybdenum may have an inhibitory effect on the enzyme. In this and in other biological processes influenced by molybdenum there appears to be a threshold molybdenum concentration below which molybdenum may have a stimulating effect and above which the effect may be inhibitory.
In animals molybdenum also influences protein synthesis, and the metabolism of phosphorus, sulfur, potassium, iron, copper, zinc, and iodine. With some animals (chicks, red trout) added dietary molybdenum stimulates growth.
Sulfate and molybdate follow similar metabolic pathways. Sulfate will alleviate molybdenum toxicity. Molybdate and sulfate act together in creating copper deficiency in cattle and sheep giving rise to the teart condition. Molybdenum inhibits the activity of the enzyme liver sulfide oxidase and the toxicity of molybdenum compounds is enhanced by sulfide. In assessing possible biological effects of molybdenum it is important to take into account its metabolic interrelationships with other trace elements.
Reid, Scott D., MOLYBDENUM AND CHROMIUM, 2012, 375-415.
2 Homeostasis and Toxicology of Essential Metals
This 473-page book in English titled "Homeostasis and Toxicology of Essential Metals" contains 9 individually authored chapters. The book highlights a list of contributors and their respective institutions. Each chapter contains a list of references. Specific topics discussed include an introduction to metals in fish physiology and toxicology, chemical speciation, characterization, toxicity, essentiality, behavioral effects of metals such as copper, zinc, iron, nickel, cobalt, selenium, molybdenum and chromium, field studies on metal accumulation and effects in fish. This book will be of use to those interested in essential metals and toxicology of essential metals.
Homeostasis and Toxicology of Essential Metals, Homeostasis and Toxicology of Essential Metals, 2012, 31A