![]() ![]() As a byproduct of this reaction, methyl-THF is converted to THF, which is converted to intermediates used in the synthesis of pyrimidine bases of DNA. Vitamin B12 is a cofactor for the enzyme methionine synthase, which is used in the conversion of homocysteine to methionine. If B12 cannot be absorbed, regardless of the etiology, many impairments may occur. Once absorbed, B12 is involved in metabolic pathways important in both neurologic and hematologic functions. The newly formed complex of B12 and intrinsic factor can then bind to receptors on the ileum, which allows for absorption of B12. Once the complex arrives at the small intestine, B12 is cleaved from R-factor by pancreatic enzymes, allowing it to bind to a glycoprotein called intrinsic factor, which is secreted by gastric parietal cells. In healthy patients, dietary vitamin B12 binds to a protein called R-factor, which is secreted from salivary glands. This activity describes the evaluation and management of vitamin B12 deficiency and highlights the role of the interprofessional team in improving care for affected patients. However, in cases in which vitamin B12 cannot be absorbed, for example, due to dietary insufficiency, malabsorption, or lack of intrinsic factor, hepatic stores are depleted, and deficiency ensues. Vitamin B12 is stored in excess in the liver, decreasing the likelihood of deficiency. Vitamin B12 deficiency can lead to hematologic and neurological symptoms. Once absorbed, vitamin B12 is used as a cofactor for enzymes that are involved in the synthesis of deoxyribonucleic acid (DNA), fatty acids, and myelin. Intrinsic factor is a glycoprotein produced by parietal cells in the stomach and necessary for the absorption of vitamin B12 in the terminal ileum. Vitamin B12, also known as cobalamin, is a water-soluble vitamin that is derived from animal products such as red meat, dairy, and eggs.
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