ABSTRACT
Pyridoxal-5′-phosphate (PLP) is an essential cofactor of transamination and decarboxylation reactions in various pathways, including biosynthesis of GABA, epinephrine, norepinephrine, serotonin and dopamine as well as degradation of glutamate and glycine [1]. It is synthesized from dietary pyridoxal, pyridoxamine, and pyridoxine (Figure 100.1). The conversion of pyridoxine and pyridoxamine to the only active cofactor, PLP, requires the activity of a kinase and then of pyridox(am)ine 5′-phosphate oxidase (PNPO); synthesis of the active cofactor from dietary pyridoxal or pyridoxal phosphate requires the kinase only. The three biologically active 2-methylpyridine derivatives collectively carry the generic name vitamin B6. In the body, pyridoxine is found primarily in the liver and muscles. PLP is a highly reactive aldehyde, whose intracellular availability must be closely regulated to saturate all newly synthesized apo-enzymes while avoiding reactions to other nucleophiles. In humans, PLP deficiency causes peripheral neuritis, dermatitis, anemia, and relevant to neurotransmitter disorders, irritability, restlessness, hyperacusis, and convulsions in the central nervous system (CNS) [2].
