J. Biochem, 1982, Vol. 91, No. 1 135-141
© 1982 Japanese Biochemical Society
research-article |
Further Physicochemical Studies on the Complex Formation between Iron-Sulfur Proteins and Flavoproteins from Spinach Chloroplast and Beef Adrenal Cortex Electron-Transfer Systems1
*Department of Biophysical Chemistry, Kitasato University School of Medicine Sagamihara, Kanagawa 228
**Suntory Central Research Institute Shimamoto Mishima, Osaka 618
***Department of Chemistry, Wayne State University Detroit, Michigan 48202, U.S.A.
Physicochemical experiments were performed in order to get further evidence of the formation of complexes between iron-sulfur proteins and flavoproteins from spinach chloroplast and beef adrenal cortex electron-transfer systems.
With both spinach and adrenal iron-sulfur protein-flavoprotein systems, characteristic difference circular dichroism (CD) spectra between the sum of CD spectra of the respective proteins and the CD spectrum of a mixture with a molar ratio of one to one were obtained in the visible and far-ultraviolet regions. By differential scanning calorimetry (DSC) measurements, ferredoxin and ferredoxin-NADP reductase were found to be stabilized against heat treatment upon mixing: (1) the apparent denaturation temperatures of ferredoxin and the reductase increased by about 18 and 5°C, respectively, and (2) the activation energy of the denaturation reaction increased by about 50%.
These results lead to the conclusion that the iron-sulfur protein and flavoprotein form a tightly bound complex, and suggest that the complex formation alters both the environments of the iron-sulfur and flavin chromophores and the contents of the ordered structures, resulting in stabilization of the proteins.
1 This work was supported in part by a research grant from the National Institute of Health (AM-l2713) to T.K.