AUTHOR Dr. Carlos Orozco (BSc, MSc, ND, MD, PhD, FPAMS).
This vitamin must be hydrolyzed from protein in order to be active. Hydrolysis occurs in the stomach by gastric acids or the intestines by trypsin digestion following consumption of animal meat.
Cobalamin is more commonly known as vitamin B12. Vitamin B12 is composed of a complex tetrapyrrol ring structure (corrin ring) and a cobalt ion in the center. Vitamin B12 is synthesized exclusively by microorganisms and is found in the liver of animals bound to protein as methycobalamin or 5′-deoxyadenosylcobalamin.
The vitamin must be hydrolyzed from protein in order to be active. Hydrolysis occurs in the stomach by gastric acids or the intestines by trypsin digestion following consumption of animal meat. The vitamin is then bound by intrinsic factor, a protein secreted by parietal cells of the stomach, and carried to the ileum where it is absorbed. Following absorption the vitamin is transported to the liver in the blood bound to transcobalamin II.
Biological Function of Vitamin B12
Vitamin B12 plays a major role in the biosynthesis of nucleic acids, DNA, protein and blood cells, the maintenance of the bone marrow, the gut mucosa, epithelial cells and lipids, the myelination of nerve and brain fibers.
Vitamin B12 and Homocysteine Metabolism S-adenosylhomocysteine is formed during S-adenosylmethionine-dependent methylation reactions, and the hydrolysis of S-adenosylhomocysteine results in homocysteine. Homocysteine may be remethylated to form methionine by a folate-dependent reaction that is catalyzed by methionine synthase, a vitamin B12-dependent enzyme. Alternately, homocysteine may be metabolized to cysteine in reactions catalyzed by two vitamin B6-dependent enzymes.
Signs, symptoms, and health problems associated with vitamin B12 deficiency
Deficiency of vitamin B12 occurs as a result of an inability to absorb vitamin B12 from food and also occurs in strict vegetarians who do not consume any foods that come from animals. As a general rule, most individuals who develop a vitamin B12 deficiency have an underlying stomach or intestinal disorder that limits the absorption of vitamin B12. Sometimes the only symptom of these intestinal disorders is subtly reduced cognitive function resulting from early vitamin B12 deficiency. Anemia and dementia follow later.
Characteristic signs and symptoms include anemia, fatigue, weakness, constipation, loss of appetite, and weight loss . Deficiency also can lead to neurological changes such as numbness and tingling in the hands and feet.
Additional symptoms of vitamin B12 deficiency are difficulty in maintaining balance, depression, confusion, dementia, poor memory, and soreness of the mouth or tongue .
Signs of vitamin B12 deficiency in infancy include failure to thrive, movement disorders, delayed development, and megaloblasticanemia.