/sup 14/C-labeled adenine aqueous solution was irradiated with /sup 60/Co gamma-rays. The yield of adenine-7-N-oxide, a radiolytic product, was determined by Sephadex G-10 column chromatography and TLC autoradiography. The apparent productive yield was very low, but the true yield should be much higher because of the reversible reaction to adenine and the easy decomposition of the N-oxide itself. Using synthesized /sup 14/C-adenine-7-N-oxide, noncovalent binding of this N-oxide to urease, an SH protein, was confirmed in comparison between the presence and absence of SDS by Ultrogel AcA 22 column chromatography. The noncovalent binding of the gamma-irradiated /sup 35/S-cysteine was also observed. The yield reached a limit in O/sub 2/ easier than in N/sub 2/ as the atmosphere for DNA irradiation. These results support an interaction structure, chemical bonds N-O---H-S-, for noncovalent binding which may be applied to the biological system as a radiation-induced damage.