Protective Effect of Sulfoquinovosyldiglyceride (SQDG) and Taurine Against Lipid Peroxidation

Abstract

Euglena gracilis Z grown under light is rich in sulfur-containing lipid, sulfoquinovosyldiglyceride (SQDG). However, the cells grown in the dark and its bleached mutant strain, SMZ that lacks chloroplasts does not accumulate as high SQDG content as E. gracilis Z grown under light. E. gracilis Z as a model of plant cell and E. gracilis SMZ as a model of animal tell were used to examine how they respond to UV-B irradiation stress. Only light-adapted E. gracilis Z was found to keep intracellular hydroperoxides level low even under UV-B exposure. We compared the antioxidative effect of SQDG and taurine both of which have common chemical structure as sulfonate group. Model experiments were made with water soluble initiator, 2,2’-azo-bis-(2-amidinopropane) dihydrochloride [AAPH] or UV-B irradiation with a peak at 312 nm in the presence of 3-hydroxykynurenine by using SQDG-embedded multilamellar liposomes or taurine-added liposome. Results showed that both in liposomes containing SQDG or taurine, AAPH-induced lipid peroxidation was significantly inhibited, but UV-B-induced lipid peroxidation was promoted in the SQDG-containing liposomes. Any significant effect was not recognized in the taurine-containing liposomes. Methylated SQDG also showed the same results as native SQDG, which suggest sulfonate group seems to have something to do with radical scavenging. In chloroplast, SQDG may play as a synergistic role for other antioxidants to prevent peroxidative damage in the light-adapted E. gracilis Z.