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Development and Growth Regulation

5'-Azido-N-1-Napthylphthalamic Acid, a Photolabile Analog of N-1-Naphthylphthalamic Acid ¹

Synthesis and Binding Properties in Curcurbita pepo L.

Department of Chemistry, Swarthmore College, Swarthmore, Pennsylvania 19081

A photolabile analog of N-1-naphthylphthalamic acid (NPA), 5'-azido-N-1-naphthylphthalamic acid (Az-NPA), has been synthesized and characterized. This potential photoaffinity label for the plasma membrane NPA binding protein competes with [³H]NPA for binding sites on Curcurbita pepo L. (zucchini) hypocotyl cell membranes with K_0.5 = 2.8 x 10^–7 molar. The K_0.5 for NPA under these conditions is 2 x 10^–8 molar, indicating that the affinity of Az-NPA for the membranes is only 14-fold lower than NPA. While the binding of Az-NPA to NPA binding sites is reversible in the dark, exposure of the Az-NPA treated membranes to light results in a 30% loss in [³H]NPA binding ability. Pretreatment of the membranes with NPA protects the membranes against photodestruction of [³H]NPA binding sites by Az-NPA supporting the conclusion that Az-NPA destroys these sites by specific covalent attachment.