SINGLET OXYGEN-MEDIATED INACTIVATION OF ACETYLCHOLINESTERASE - A COMPARISON OF PURIFIED ENZYME IN SOLUTION AND ENZYME-BOUND TO K562 LEUKEMIA-CELLS

We have compared the singlet oxygen-mediated inactivation of acetylcho linesterase (ACE) in solution with the inactivation of ACE on the surf ace of K562 leukemia cells, In solution, the actions of the singlet-ox ygen quenchers, methionine, azide, disodium ene-bis(5-sulfosalicyliden eimminato)]nickelate(II) (Ni-chelate 1) and disodium [(N,N'-2,3-propio nic cid)bis(5-sulfosalicylideneimminato)]nickelate(II) (Ni-chelate 2) could be explained quantitatively by assuming their only mechanism of action was to quench singlet oxygen, The singlet oxygen quenchers, azi de, Ni-chelate 1 and Ni-chelate 2, caused smaller inhibitions in the r ate of singlet oxygen-mediated inactivation of ACE on K562 cells than ACE in solution, The effects of these quenchers and of deuterium oxide were interpreted using a mathematical model of singlet-oxygen quenchi ng and diffusion to estimate the lifetime of singlet oxygen near the c ell surface, The azide quenching data and the deuterium-oxide data gav e lifetimes of 0.9 +/- 0.2 mu s and 0.45 +/- 0.15 mu s, respectively, The increases in ACE inactivation lifetime caused by the nickel chelat es were anomalously large, The unexpectedly large quenching due to the nickel chelates may have been due to a nonuniform distribution of the chelates in the cytoplasm with a large concentration of the chelate n ear the cell membrane.