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Conversion of vitamin B6 vitamers into the active form of vitamin B6

Only dephosphorylated B6 vitamers can enter (or exit) the cell. Once inside the cell, pyridoxal kinase (PDXK) phosphorylates the different vitamers, yielding pyridoxine-5’-phosphate (PNP) from pyridoxine (PN), pyridoxamine 5’-phosphate (PMP) from pyridoxamine (PM), and pyridoxal 5′-phosphate (PLP) from pyridoxal (PL). PNP and PMP are both converted to the active form of vitamin B6, PLP, by pyridoxine 5′-phosphate oxidase (PNPO). Pyridoxal phosphatase (PDXP), along with other phosphatases, hydrolyze phosphorylated vitamin B6 vitamers, enabling them to exit the cell. Legend: ALPL, tissue-nonspecific alkaline phosphatase; PDXK, pyridoxal kinase; PDXP, pyridoxal phosphatase; PL, pyridoxal; PLP, pyridoxal 5′-phosphate; PM, pyridoxamine; PMP, pyridoxamine 5’-phosphate; PN, pyridoxine; PNP, pyridoxine-5’-phosphate; PNPO, pyridoxine 5′-phosphate oxidase. (Contributed by Dr. Douglas Lanska.)

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