Abstract
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 [(3)H]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 [(3)H]NPA binding ability. Pretreatment of the membranes with NPA protects the membranes against photodestruction of [(3)H]NPA binding sites by Az-NPA supporting the conclusion that Az-NPA destroys these sites by specific covalent attachment.