B6 metabolism. Pyridoxine and pyridoxamine are derived from vegetables and meat, respectively. These two are ultimately converted into pyridoxal-5-phosphate (P5P) by PNPO. Defects in antiquitin, an enzyme in the lysine degradation pathway, are the cause of pyridoxine-responsive seizures leading to accumulation of the upstream intermediary alpha-aminoadipic semialdehyde (AASA) and sequestration of P5P. P6C, piperideine-6-carboxylic acid; ALDH7A1, antiquitin or aldehyde dehydrogenase 7 family, member A1.