Dehydroascorbic acid DHA gives a pentacyclic dimer structure of indefinite stability. Recycling of ascorbate via active transport of DHA into cells, followed by reduction and reuse, mitigates the inability of humans to synthesize it from glucose. Vitamin C accumulates in mitochondria, where most of the free radicals are produced, by entering as DHA through the glucose transporters, GLUT10. Ascorbic acid protects the mitochondrial genome and membrane. Vitamin C does not pass from the bloodstream into the brain, although the brain is one of the organs that have the greatest concentration of vitamin C. Instead, DHA is transported through the blood–brain barrier via
Vitamin B6 pyridoxal and pyridoxamine. Vitamin B was named pyridoxine to indicate its structural homology to pyridine. Vitamin B6 Vitamin B refers to a group of chemically similar compounds which can be interconverted in biological systems. Vitamin B is part of the vitamin B group of essential nutrients. Its active form, pyridoxal 5′-phosphate, serves as a coenzyme in some 100 enzyme reactions in amino acid, glucose, and lipid metabolism. All forms except pyridoxic acid and pyritinol can be interconverted. Absorbed pyridoxamine is converted to PMP by pyridoxal kinase, which is further converted to PLP by pyridoxamine-phosphate transaminase or pyridoxine 5′-phosphate oxidase which