Pyridoxine (PN) is the C4 hydroxymethyl derivative, pyri-doxal (PL) is the C4 formyl derivative and pyridoxamine (PM) is the C4 aminomethyl derivative of 5-(hydroxymethyl)-2-methylpyridin-3-ol). Each of these are also converted to their corresponding 5'-phosphate derivatives referred to as pyridoxine 5'-phosphate (PNP), pyridoxal 5'-phosphate (PLP), and pyridoxamine 5' -phosphate (PMP), respectively (see Fig. 28.34). Because of their ability to interconvert, all are considered active forms of vitamin B6 in vivo. Although PLP is the major coenzyme form, PMP can also function as a coenzyme primarily in aminotransferases. The major metabolite is 4-pyridoxic acid, which is excreted in the urine.
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