title: Singlet oxygen-mediated inactivation of acetylcholinesterase: a comparison of purified enzyme in solution and enzyme bound to K562 leukemia cells.
abstract: We have compared the singlet oxygen-mediated inactivation of acetylcholinesterase (ACE) in solution with the inactivation of ACE on the surface of K562 leukemia cells. In solution, the actions of the singlet-oxygen quenchers, methionine, azide, disodium [N,N'-ethylenebis (5-sulfosalicylideneimminato)]nickelate(II) (Ni-chelate 1) and disodium [(N,N'-2,3-propionic acid)bis(5-sulfosal-icylideneimminato)] 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, azide, Ni-chelate 1 and Ni-chelate 2, caused smaller inhibitions in the rate 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 quenching and diffusion to estimate the lifetime of singlet oxygen near the cell surface. The azide quenching data and the deuterium-oxide data gave lifetimes of 0.9 +/- 0.2 microsecond and 0.45 +/- 0.15 microsecond, respectively. The increases in ACE inactivation lifetime caused by the nickel chelates 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 near the cell membrane.
authors.affiliation: Hines Veterans Affairs Hospital, IL 60141, USA.
authors.forename: G
authors.initials: G
authors.lastname: Deadwyler
authors.forename: P D
authors.initials: PD
authors.lastname: Sima
authors.forename: Y
authors.initials: Y
authors.lastname: Fu
authors.forename: J R
authors.initials: JR
authors.lastname: Kanofsky
mesh_terms: D000110:Acetylcholinesterase / Q000378:metabolism*; D000818:Animals; D001386:Azides / Q000494:pharmacology; D002800:Cholinesterase Inhibitors / Q000378:metabolism*; D006801:Humans; D004915:Leukemia, Erythroblastic, Acute / Q000201:enzymology* / Q000378:metabolism; D051379:Mice; D008956:Models, Chemical; D010100:Oxygen / Q000378:metabolism*; D010777:Photochemistry; D011994:Recombinant Proteins / Q000378:metabolism; D026082:Singlet Oxygen; D012996:Solutions; D013499:Surface Properties; D014407:Tumor Cells, Cultured
chemical_list: D001386:Azides; D002800:Cholinesterase Inhibitors; D011994:Recombinant Proteins; D012996:Solutions; D026082:Singlet Oxygen; D000110:Acetylcholinesterase; D010100:Oxygen