Pyridoxal phosphate (PLP, pyridoxal 5'-phosphate, P5P) is the active form of vitamin B6 and is a coenzyme in many enzymatic reactions. The International Union of Biochemistry and Molecular Biology has cataloged more than 140 PLP-dependent activities, equivalent to 4% of all taxonomic activities. [3] The versatility of PLP stems from its ability to covalently bind substrates, which then act as electrophilic catalysts, thereby stabilizing different types of carbanion reaction intermediates.

GABA (gamma-aminobutyric acid) metabolism and biosynthesis. Pyridoxal phosphate is a cofactor for glutamate decarboxylase (GAD). This allows for the conversion of glutamate to GABA. The termination response of GABAergic neurons occurs in the cytoplasm, so vitamin B6 deficiency may contribute to seizures in children. Pyridoxal phosphate is also involved in the oxidative deamination of GABA and is a cofactor for GABA transaminase.
Ornithine metabolism. Pyridoxal phosphate is a cofactor for ornithine carboxylase.
Transamination. Pyridoxal phosphate is involved in the decomposition and synthesis of amino acids.