Cobalt is necessary for vitamin B12 activity and is incorporated into its corrin ring. It is present in two coenzymes involved in methylation reactions. A cobalt deficiency results in vitamin B12 deficiency and megaloblastic anemia. Chromium facilitates glucose metabolism and lipid transport as part of its role in insulin function. It lowers cholesterol and raises HDL levels. Nickel activates some enzymes while inhibiting others and is required for growth, but deficiency in humans is unknown. Toxicity of excess amounts can damage organs.

1. Metabolism of Cobalt, Chromium & Nickel
Gandham. Rajeev

2. Cobalt
• Cobalt is necessary for biological activity of
vitamin B12.
• Cobalt fits into the corrin ring of vitamin B12.
• Sources:
• Liver, pancreas and vitamin B12.
• RDA:
• 1µg/day

3. Functions
• Cobalt is a constituent of cobalamin or vitamin B12.
• Vitamin B12 is present in 2 coenzymes of cobalamin
• Methylcobalamin and 2-deoxyadenosyl cobalamin.
• Methylcobalamin is a cofactor for homocysteine
methyl transferase.
• 2-deoxyadenosyl cobalamin is a cofactor for L-
methylmelonyl CoA mutase.

4. • Deficiency:
• A cobalt deficiency is accompanied by all
the signs and symptoms of a vitamin B12.
• Vitamin B12 deficiency results in
megaloblastic anemia.
• Toxicity:
• Excess levels of cobalt results in
polycythaemia.

5. Chromium
• The adult human body contains about 6 mg.
• Sources:
• Brewer’s yeast, molasses, meat products,
cheese, whole grains.
• RDA:
• 0.05 to 20 mg/day

6. Absorption and excretion
• The biologically active form of chromium
(Cr3+) is absorbed poorly from the diet.
• The majority of orally absorbed chromium is
excreted through urine.

7. Functions
• In association with insulin, Cr promotes the
utilization of glucose,
• Cr is a component of a protein – chromodulin,
which facilitates the binding of insulin to cell
receptor sites.
• Cr lowers the total cholesterol level.
• Cr decreases serum LDL levels & increases
HDL levels.
• Cr participates in transport of amino acids.

8. Deficiency
• Causes:
• Malnutrition & malabsorption.
• Features;
• Impaired glucose tolerance in malnourished
children, and diabetes in elderly persons.
• Toxicity:
• Excess intake of Cr results in toxicity, leading
to liver & kidney damage.

9. Nickel
• Source and distribution:
• Nickel occurs trace amounts in human &
animal tissues.
• Nickel does not accumulate with age in any
of human tissue other than lungs.
• It is poorly absorbed from intestine.
• It is excreted mainly through faeces.

10. Functions
• Nickel activates some enzymes such as
arginase & urease.
• It also inhibits some enzymes such as acid
phosphatase.
• Nickel is required in trace amounts for
growth and reproduction.

11. Deficiency & Toxicity
• Nickel deficiency in humans is unknown.
• In experimental animals impaired growth &
reproduction, anemia.
• Toxicity:
• Nickel is relatively non-toxic.
• Prolonged exposure results in respiratory
tract neoplasia & dermatitis.

12. Reference books
• Text book of Biochemistry - U Satyanarayana
• Text book of Biochemistry – DM Vasudevan
• Text book of Biochemistry - MN Chatterjea

13. Thank you