title: Quantitation of the singlet oxygen produced by UVA irradiation of human lens proteins.
abstract: Ultraviolet irradiation of aged human lens proteins in vitro causes extensive photolytic damage of His and Trp residues. Protection by sodium azide argues for a process mediated by singlet oxygen (1O2). In the work described here, the synthesis of 1O2 was measured by the bleaching of N,N-dimethyl-4-nitrosoaniline (RNO), the oxidation of added histidine and the oxidation of furfuryl alcohol. To obtain a more accurate value for 1O2 generation, a known quantity of 1O2 was generated by the thermal dissociation of 3-(4-methyl-naphthyl)propionic acid endoperoxide, and the efficiency of each assay method to report on the 1O2 generated was determined. The values obtained were 0.003 mol of RNO bleached/mol of 1O2 generated, 0.55 mol of furfuryl alcohol oxidized/mol 1O2 and 0.5 mol of His oxidized/mol 1O2 generated. Irradiation of the human lens proteins with UVA light produced from 2.1 to 2.4 mM of 1O2 by RNO bleaching, 2.6-2.8 mM 1O2 by furfuryl alcohol oxidation and up to 1.9 mM of 1O2 by histidine oxidation during a 1 h irradiation period. The average value (2.2 mM of 1O2) corresponds to the theoretical production of 30 nmol of singlet oxygen at UVA light intensities equivalent to a 1 h exposure to sunlight at noon in the northern hemisphere.
authors.affiliation: Mason Eye Institute, University of Missouri, Columbia 65212, USA.
authors.forename: M
authors.initials: M
authors.lastname: Linetsky
authors.forename: B J
authors.initials: BJ
authors.lastname: Ortwerth
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D003459:Crystallins / Q000737:chemistry / Q000528:radiation effects*; D006801:Humans; D010100:Oxygen / Q000032:analysis*; D026082:Singlet Oxygen
chemical_list: D003459:Crystallins; D026082:Singlet Oxygen; D010100:Oxygen