What does Vitamin B12 do in the body?
Vitamin B12 comes in many forms. Only two forms are used in the human body, Methylcobalamine and 5-deoxyadenosylcobalamine.
Vitamin B12, as methylcobalamine is required with folate for the enzyme methionine synthase to produce methionine from homocysteine. Inadequate methionine synthase can lead to an accumulation of homocysteine. Excessive homocysteine has been associated with an increased risk of heart disease.
Methionine also helps to add methyl groups to different compounds including proteins, phospholipids, DNA and RNA. Methylated genes in DNA and RNA are ‘Off’ while unmethylated genes are considered ‘On.’ Methylation and therefore vitamin B12 may have a role in cancer prevention.
In nerve cells, methionine is required for the methylation of myelin basic protein (MBP) and myelin phospholipids. MBP and myelin phospholipids are building blocks for the production and maintenance of myelin sheaths which surround neuronal axons. The myelin sheaths allow for not only faster transmission of signals down the nerves but for the transmission of signals at all.
Succinyl-Co A production–
Vitamin B12, as 5-deoxyadenosylcobalamine, is required by the enzyme L-methylmalonyl-coemzyme A mutase. This enzyme takes L-methylmalonyl-coenzyme A to produce succinyl-coenzyme A (succinyl-CoA). Allowing for and promoting the production of succinyl-CoA is the likely mechanism behind the energetic feeling one gets from vitamin B12.
The coenzyme A is a large molecule used by the body to assist other enzymes in the synthesis and oxidation of fatty acids. Coenzyme A can be produced by the body from vitamin B5 (pantothenate).
Succinyl-CoA has two major roles in the body. First, succinyl-CoA is a step in the citric acid or Krebs cycle (finished by Hans Adolf Krebs while working at the University of Sheffield in 1937). The Krebs cycle allows the body to produce energy from glucose, fatty acids or amino acids. Conversely, the Krebs cycle can provide intermediates for the production of glucose and some amino and fatty acids.
Second, succinyl-CoA, along with glycine, provides the material for the initial step in heme synthesis. Heme is a molecule which enables the body to hold and use iron. When combined with a globin protein, heme forms hemoglobin which allows the red blood cells to transport oxygen throughout the body. Heme can also be combined with a different globin protein in the muscles producing myoglobin. Myoglobin holds oxygen in the muscles to be used for energy production. The heme molecule is also used by the body to produce other important proteins such as cytochrome c (produces ATP (energy for cells) from electron transport in the mitochondria), catalase (converts dangerous hydrogen peroxide to harmless water and oxygen) and endothelial nitric oxide synthase (produces nitric oxide (NO) which relaxes blood vessels and prevent platelet aggregation.