Pyrroloquinoline quinone-13C3 (sodium) is an isotope of Pyrroloquinoline quinone. Pyrroloquinoline quinone (PQQ), a redox co-factor, is an anionic, redox-cycling orthoquinone. Pyrroloquinoline quinone is isolated from cultures of methylotropic bacteria and tissues of mammals. Pyrroloquinoline quinone is an essential nutrient for mammals and is important for immune function.