EFFECTS OF NEUTRAL SALTS ON THERMAL-STABILITY OF SPINACH FERREDOXIN

The effects of various neutral salts on the thermal stability of spinach ferredoxin were studied by means of differential scanning calorimetry and circular dichroism. Upon addition of 1 M NaCl, the apparent denaturation temperature increased by about 13°, and the enthalpy and activation energy for the denaturation also increased by 27% and 44%, respectively. The salt effect was ascribed essentially to the ionic strength of the environment. The circular dichroism measurements showed that the interaction between the iron-sulfur cluster and the protein moiety was modulated by the salt, resulting in stabilization of the protein, It is therefore highly probable that the native ferredoxin structure is maintained through the interaction with the iron-sulfur chromophore. © 1979 Academic Press, Inc. All rights of reproduction in any form reserved.