ISSN:
1573-904X
Keywords:
superoxide dismutase
;
lipid membranes
;
FT-IR
;
conformation
;
thermal stability
;
curve-fitting
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract Purpose. Superoxide dismutase (SOD), an antioxidant enzyme, converts peroxide radicals into hydrogen peroxide. Liposomes have been used as carriers for SOD to enhance its antioxidant effect. Our previous DSC study has suggested that SOD binding to dipalmitoylphosphatidylglycerol (DPPG) may protect lipid membranes against oxygen-mediated injury. We now present FT-IR studies on the effect of DPPG binding on the temperature-induced SOD folding-unfolding process. Methods. The FT-IR spectra of SOD in D2O or DPPG membranes are measured as temperatures increase from 28° to 121°C at a rate of 0.5°C/ min. From the quantitative determination of the changes in the amide I band components of the Fourier self-deconvoluted spectra, the DPPG-induced changes of SOD secondary structure could be detected as a function of temperature. Results. We observe that the relative intensity of the SOD bands from 28°C to 77°C show graduate loss of β-sheet “distorted” structure, loss of turns, and existence of an intermediate state around 50°C. Beginning at 80°C, changes are obtained in three temperature regions: (i) 80°C, (ii) 92°C, (iii) 109°C. The result suggests that SOD folding/unfolding transition involves mostly the relative changes within the regions of helix-like hydrogen bonding pattern, turn, twisted β-bend and irregular structures. When SOD is bound to DPPG, the conformational changes shift to lower temperatures, indicating a reduction of SOD thermal stability. In addition, the gel to liquid crystalline phase transition temperature of DPPG increases from 42°C to 43.5°C. Conclusions. These results suggest that the thermal stability of SOD is reduced by DPPG binding. However, DPPG bilayer is stabilized by the presence of SOD.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1016099232745
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