Molybdenum

SourcesContent depends on the concentration of Mo

in the soil

Found in larger amounts in black beans, walnuts and lentils

Also in spinich, lettuce, whole wheat pasta and bread

Absorption, Transport and StorageAbsorption increases as dietary intake of Mo

increases. (22-1490 µg/day)

Mo is transported in the blood as molybdate which is bound to albumin/ alpha-2 macroglobumin

Mo is found in the tissues as molybdate, free molybdopterin or molybdopterin bound to enzymes

Mo can be found in high amounts and concentrations in the liver, kidneys and the bone.

Also found in lower amounts and concentrations in the small intestine, lungs, spleen, brain, thyroid, adrenal glands and muscle

Functions and Mechanisms of ActionMolybdopterin functions as a cofactor for the

metalloenzymes (sulfite oxidase, aldehyde oxidase, xanthine deydrongenase and xanthine oxidase)

It allows for Mo to bind to the catalytic site of the apo-enzyme

Molybdopterin carries the Mo to the apoenzyme at its catalytic site where it undergoes further bonding

Dioxomolbdopterin is formed as the Mo is further bonded to 2 Oxygen molecules

Oxosulfidomolybdopterin is formed as the Mo is further bonded to one Oxygen and one Sulphur

Sulfite OxidaseLocated in the mitchondrial inner membrane

Found in tissues of the heart, liver and kidney

Contains iron sulphur clusters, 2 molybdopterins in the dioxo form and 2 cytochrome residues.

Catalyzes the terminal step in metabolism of methionine and cysteine. During this process sulfite is converted to sulfate

The sulfite may be supplied through the diet because it is used as an antimicrobial agent during processing.

The sulfate produced is excreted in the urine or is used for the synthesis of sulfolipids, sulfoproteins and mucopolysaccharides

Aldehyde OxidaseThe enzyme uses the oxosulfido form of

molybdpterin

Functions in the liver whereby it uses O2 as it electron acceptor

Substrates used in this reaction are compounds containing an aldehyde to generate carboxylic acids

aldehyde + H2O + O2 <=> a carboxylate + H2O2 + H+

Xanthine Dehydrogenase(XD) and Xanthine Oxidase(XO)Both enzymes are iron dependant which

require FAD and molybdopterin (oxosulfido form)

XD is found in the tissues in the lungs, intestine, liver and kidneys

XO is mainly in the intestines and thyroid cells

The enzymes are capable of hydroxylating purines, pyrimidines and other heterocyclic N containing Compounds

Hypoxanthine generated from purine catabolism is oxidized to form xanthine and uric acid

XD e- are transferred from the substrate to NAD+ to generate NADH + H+

XO O2 accepts (e-) from FADH2 and H2O2

Human disorder known as xanthinuria (Larger amts of xanthine are excreted in the urine)

Higher concentrations of xanthine in the urine can cause the formation of kidney stones

Excretion Mo is excreted as molybdate mainly in the

urine. It is excreted in smaller amounts in the feces (with the interaction Mo of bile), sweat (20µg) and the hair (0.01µg/g hair)

Excretion increases as dietary Mo intake increases

Hence little Mo is absorbed in the body

RDA for MoInfants 0-0.5= 2µg“ “ “ “ 0.5-1=3µgChildren 4-8= 22µgMale and Female 9-13= 34µg“ “ “ “ “ “ “ “ 14-18= 43µg“ “ “ “ “ “ “ “ 19- >70= 45µgPregnant women = 50µg

DeficiencyIn China it has been documented with low

Mo has been linked with esophageal cancer

Congenital Mo cofactor deficiency disease in infants disrupts the body’s use of Mo in the metalloenzymes

ToxicityMo is relatively non toxic with intakes of

1500µg per day.

Possible to experience syntoms of gout (accumulation of uric acid in the joints resulting in inflammation)

Occurs due to high concentrations of uric acid from XO and XD activity

References

http://minerals.usgs.gov/minerals/pubs/commodity/molybdenum/

http://www.lenntech.com/periodic/elements/mo.htm

http://www.cancer.org/Treatment/TreatmentsandSideEffects/ComplementaryandAlternativeMedicine/HerbsVitaminsandMinerals/molybdenum