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

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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.)