SONOCHEMISTRY OF CYTOCHROME-C - EVIDENCE FOR SUPEROXIDE FORMATION BY ULTRASOUND IN ARGON-SATURATED AQUEOUS-SOLUTION

Formation of superoxide anion radicals (O-2(.-)) induced by 50 kHz ult rasound in argon (Ar)-saturated aqueous solution was studied. Although EPR-spin trapping study with 5,5-dimethyl-1-pyrroline N-oxide (DMP0;1 00 mM) revealed the formation of DMPO-adducts of hydroxyl radicals ((O H)-O-.) and hydroperoxy radicals (HO2; acid form of O2(.-)) in O-2-sat urated solution after sonication, no evidence of HO2.- was found in Ar -saturated solution. When ferricytochrome c (cytochrome c) in Ar-satur ated aqueous solution was sonicated, the reduced form of cytochrome c was observed and 80% of its formation was inhibited by the addition of superoxide dismutase (SOD). Sodium formate enhanced the production of the reduced form of cytochrome c. The % inhibition by SOD for the red uction increased in the order of Xe > Ar > He in accord with the highe r temperatures of the cavitation bubbles. These results indicate that the O-2(.-) is formed by directly by the sonolysis of water in the abs ence of O-2 when the temperature of cavitation bubble collapse is suff iciently high.