Vitamin B6 (pyridoxine, pyridoxal, pyridoxamine) biosynthesis and salvage pathway (Zea mays)

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Several forms of the vitamin are known, but pyridoxal 5’-phosphate (PLP) is the biologically active form and is a cofactor in various reactions of amino acid metabolism, including transamination, deamination, and decarboxylation, racemization and others. In plants PLP is synthesized de novo in the cytosol by the two-protein (PDX1/PDX2) PLP synthase complex from pentose phosphate, triose phosphate, and glutamine pre-cursors (reviewed in Fitzpatrick, 2011). PLP can also be made in chloroplasts or cytosol from pyridoxamine 5'-phosphate (PMP) or pyridoxine 5'-phosphate (PNP) by the salvage enzyme pyridoxamine 5'-phosphate oxidase. Pyridoxine glucosides are major forms of vitamin B6 in plants (Gregory and Ink, 1987). The details of vitamin B6 biosynthesis (especially its compartmentation) in plants are far from being elucidated. This diagram is an attempt to capture the current state of the art