We designed and synthesized a photocontrollable peroxynitrite (ONOO-) generator, P-NAP, which has N-methyl-N-nitrosoaminophenol structure with four methyl groups photodecomposition product with ONOO- and to lower the introduced onto the benzene ring to block reaction of the semiquinoneimine's redox potential. The semiquinoneimine intermediate generated by photoinduced release of nitric oxide (NO) reduces dissolved molecular oxygen to generate superoxide radical anion (O-2(center dot-)), which reacts with NO to afford ONOO- under diffusion control (k = 6.7 X 10(9) M-1 s(-1)). NO release from P-NAP under UV-A (330-380 nm) irradiation was confirmed by ESR spin trapping. Tyrosine nitration, characteristic of ONOO-, was demonstrated by HPLC analysis of a photoirradiated aqueous solution of P-NAP and N-acetyl-L-tyrosine ethyl ester. ONOO- formation was confirmed with a ONOO--specific fluorogenic probe, HKGreen-3, and compared with that from 3-(4-morpholinyl)sydnonimine hydrochloride (SIN-1), which is the most widely used ONOO- generator at present. The photoreaction of P-NAP was influenced by superoxide dismutase, indicating that generation of O-2(center dot-) occurs before ONOO- formation. The quantum yield for formation of duroquinone, the main P-NAP photodecomposition product, was measured as 0.86 +/- 0.07 at 334 nm with a potassium ferrioxalate actinometer. Generation of ONOO- from P-NAP in HCT-116 cells upon photoirradiation was successfully imaged with HKGreen-3A. This is the first example of a photocontrollable ONOO- donor applicable to cultured cells.