Pyridoxal-5-phosphate is the metabolically active coenzyme form of vitamin B6 (pyridoxine) and accomplishes numerous biological functions. Pyridoxal-5-phosphate’s actions mainly involve the metabolism of amino acids and other nitrogen compounds. In the liver, pyridoxal-5-phosphate is essential for glucose production from amino acids through its role as a coenzyme for the transaminase enzymes. Pyridoxal-5-phosphate is also needed in the liver and muscles to access stored glycogen for glucose production, and to synthesize niacin from the amino acid tryptophan. In red blood cells, pyridoxal-5-phosphate is needed for hemoglobin synthesis and the regulation of oxygen affinity. Moreover, cell receptivity to steroid hormones is influenced by pyridoxal-5-phosphate. In the nervous system, pyridoxal-5-phosphate is needed for synthesis of several neurotransmitters, including serotonin (from tryptophan), taurine, dopamine, norepinephrine, histamine, and gammaaminobutyric acid (GABA).