Photoreactivation of superoxide dismutase by intensive red (laser) light

The effects of helium-neon laser (HNL) on activity, absorption spectra, and ESR signals of superoxide dismutase (SOD; E Cul.15.1.1) from bovine erythrocytes in acid medium were investigated. It was found that incubation during 2 hours at pH 5.9 led to inactivation of the enzyme. The subsequent illumination of SOD by HNL brought about the enzyme reactivation. Both absorption and ESR spectra were changed after incubation at pH 5.9 and restored after laser irradiation. In a model system, copper-histidine complex, absorption maximum was shifted from 632-633 nm at pH 5.8 to 639-640 nm at pH 8.5-9.0. The similar shift of the maximum was observed after illumination by HNL at pH 5.8. It may be postulated that the photoreactivation of SOD consists essentially in deprotonation of His-61 residue in the enzyme active site and subsequent recovery of imidasol bridge between copper and zinc which had been destroyed at low pH. Since many other enzymes possess similar histidine-copper structures in their active sites, one may expect diverse effects of red (laser) light on the enzyme activity. Heme-containing enzyme, catalase was also found to be photoreactivated by HNL after inactivation at pH 6.0.