A mechanism for liposome-recruited activity of oxidized and fragmented superoxide dismutase (Fr.-SOD) [Tuan LQ, Umakoshi H, Shimanouchi T, Kuboi R. Liposome-recruited activity of oxidized and fragmented superoxide dismutase. Langmuir 2008;24:350-4] was further investigated, focusing on the secondary structure of Fr.-SOD. Liposome membrane was found to assist the conformational change of Fr.-SOD and reactivate the enzymatic activity. like molecular and metal chaperones. The loss of SOD activity and its secondary structure was observed during 6 h oxidation in 2 mM hydrogen peroxide. The contents of the alpha-helix and beta-sheet structures in the oxidized and fragmented SOD (2 mu M) were increased only in the presence of 10 mu M Cu2+ and Zn2+ together, or in the presence of 2 mM POPC liposomes. The mixture of all of these elements (fragmented SOD and POPC liposomes with Cu2+ and Zn2+) gave not only the increase of the alpha-helix and beta-sheet contents but also the mediation of the high SOD-like activity. (c) 2008 Published by Elsevier Inc.