EFFECTS OF NA+ AND MG2+ ON THE THERMAL-DENATURATION OF NATIVE AND ACETYLATED SPINACH FERREDOXINS

The effects of metal ions on the thermal denaturation and Mg2+ binding of native spinach ferredoxin and its acetylated derivative were investigated.The denaturation of ferredoxin in a metal-free solution at 40°C was quickly prevented by the addition of Mg2+ or Na+ at appropriate concentrations. The metal concentrations required for 50% protection from thermal denaturation were 1.54 x 10-4 m Mg2+ or 8.0 x 10-3 m Na+ for native ferredoxin and 1.05 x 10-3 m Mg2 or 6.0 x 10-2 Mg Na+ for acetylated ferredoxin. It was also found that native ferredoxin in the presence of over 20 mM Mg2+ was almost completely protected from thermal denaturation at 40°C.The D-form which has been observed in acetylated ferredoxin by Masaki et al. (1977) (J. Biochem. 81, 1-9) was confirmed to be present in native ferredoxin at high temperature (49°C) and is suggested to be an important form in the denaturation processes of the ferredoxin molecute. © 1979, by the Japanese Biochemical Society.