Photoinactivation of Superoxide Synthases of the Plasma Membrane from Rose (Rosa damascena Mill.) Cells

The UVC-induced synthesis of hydrogen peroxide (H₂O₂) by cultured rose (Rosa damascena Mill, cv Gloire de Guilan) cells is inhibited by broad-band radiation containing UVA, UVB and blue wavelengths. In order to understand the basis for this inhibition, we tested the effects of broad-band radiation and of monochromatic radiation on NADH- and NADPH-dependent O₂- synthases of purified plasma membranes. Both activities were inhibited by wavelengths from 254 to 435 nm, with the NADPH-dependent enzyme being more sensitive than the NADH-dependent enzyme. Incubation in the presence of flavin adenine dinucleotide had a small but significant ameliorative effect on the inhibition of the O₂- synthase activities of plasma membranes by 300 nm radiation. The data support the hypothesis that the NADH- and NADPH-dependent activities are catalyzed by different enzymes. The NADPH-dependent activity, but not the NADH-dependent activity, was sufficiently sensitive to account for the inhibition of H₂O₂ synthesis by the broad-band radiation.