1-N-Naphthyl Phthalamic Acid (NPA)

Structure of 1-N-Naphthyl Phthalamic Acid (NPA)



NPA is a potent inhibitor of polar auxin transport. Stock solution 10 mM in dimethyl sulfoxide. Store at -20°C. Effective concentrations to inhibit are in the range of 1-10 µM

Molecular Target:

Binding sites in the plasma membrane, Kd of binding around 7. NPA blocks auxin efflux.


In contrast to TIBA, NPA does not cause bundling of actin in animal cells, but does so in plant cells. It is therefore thought to bind the efflux carrier. So far, no evidence for binding of NPA to PIN-proteins.

Physiological Effects:

Further reading

Katekar GF, Nave JF, Geissler AE (1981) Phytotropins. III. Naphthylphthalamic Acid Binding Sites On Maize Coleoptile Membranes As Possible Receptor Sites For Phytotropin Action. Plant Physiol 68, 1460-1464. Molecular properties, binding constants, structure-function relationship of different phytotropins.

Imhoff V, Muller P, Guern J, Delbarre A (2000) Inhibitors of the carrier-mediated influx of auxin in suspension-cultured tobacco cells. Planta (2000) 210: 580-588. Structure-function relationship for transport of 2,4-D and NAA in tobacco cells.