Animals cannot synthesize pyridoxal 5'-phosphate (PLP) which is a ligand in aminotransferases and other enzymes. PLP's accessible derivatives pyridoxine, pyridoxal, and pyridoxamine are traditionally called vitamins B6. They are taken up nutritionally from bacteria and plants, but also created from PLP in the body. The pathways used to recycle PLP from these three compounds can therefore be called vitamin B6 activation as well as PLP salvage. Because of the close similarity of the molecules, only two enzymes are needed for the task (McCormick & Chen, 1999).