Vitamin B 6 is also known as pyridoxine. It is involved in a wide range of metabolic, developmental and physiologic processes. The three compounds that show vitamin B6 activity include pyridoxine, pyridoxal and pyridoxamine. All these molecules are present in food and are converted to pyridoxal-5-phosphate (PLP) the most active form of vitamin B 6. Pyridoxine is stable to heat and sensitive to heat and alkali. Pyridoxal phosphate the active form of vitamin B6 gives vitamin B6 its various functions. It has a wide array of functions; it acts as a prosthetic group or coenzyme of various enzymes involved in metabolic processes such as transamination, decarboxylation, transsulfaration, desulfaration and non-oxidative deamination reactions. It also plays an essential role in the synthesis of heme, niacin, neurotransmitter, connective tissues, and sphingolipids in nerve sheaths as elaborated.
To begin with, pyridoxine functions as an enzymatic co-factor. It is a suitable cofactor for various biochemical reactions due to its water solubility and high reactivity when phosphorylated. VitB6 takes part in more than 140 enzymatic reactions. Most of the PLP-dependent enzymes catalyze important steps in the amino acid metabolism, for instance co-catalyzing transamination, racemization, decarboxylation, and alpha ,beta-elimination reactions. A good example of PLP cofactor function is in the regulation of steroid hormone action.
Apart from its function as a potent cofactor for PLP-dependent enzymes, pyridoxine is also thought to act directly as a protective agent against free radicals such as reactive oxygen species, like singlet oxygen hence playing a significant role as an antioxidant. In fact, Vitamin B 6 is more potent than tocopherols or carotenoids in its ability to neutralize the reactive oxygen species. As such, it prevents damage to the cellular membranes that can result in reversible cell death and hence harm the body.
It is also essential in the formation of neurotransmitters such as GABA, serotonin and catecholamines.. For instance, pyridoxal phosphate acts as a co-enzyme of glutamate de-carboxylase that converts glutamate to gamma-aminobutyrate (GABA).Deficiency therefore, results in seizures in children due to decreased formation of the neurotransmitters. However, in high amounts it can cause nerve damage. In children especially it is necessary for the normal development of the central nervous system.
Vitamin B6 in the form of PLP is necessary for the metabolism of proteins, sugar and fatty acids as well. This occurs through the transfer of amino and sulfur groups. Vital polyunsaturated fatty acids are synthesized through the desaturation of linoleic acid and gamma linolenic acid. Storage carbohydrates such as glycogen are broken down under the cofactor activity of PLP. It also has an immunosupportive function. It is necessary for a healthy immune system. Pyridoxine is also crucial for mounting an effective immune response through stimulation of the immune cells. Deficiency in pyridoxine has been shown to alter the immune response.
Pyridoxine is also important for the cardiovascular health. Just like folates and cobalamines, it helps to reduce the levels of homocsyteine an intermediate in methionine metabolism. A PLP dependent enzyme helps convert homocsyteine to methionine. Homocysteine is considered a risk factor for atherosclerosis and venous thrombosis. Also has a role in reduction of high blood pressure.
Vitamin B 6 is essential for the activation of glycine in the initial stages of heme production which makes it a key molecule in the formation of hemoglobin. As such, deficiency could result in anemia. Vitamin B 6 is also essential for growth and maintaining a healthy skin. Deficiency may result in poor skin health such as the occurrence of skin lesions.
Indeed, pyridoxine is essential for the cellular metabolism and general well-being of all living organism. The recommended daily allowance in adults is mainly determined by the amount of protein intake. For adults, it is a minimum of 2 mg of B6 per 100grams of consumed protein, whereas in children it ranges from 0.6 to 1.2 mg per 100 grams of protein. Nonetheless, pyridoxine deficiency is rare.