EurekaMag.com logo
+ Site Statistics
References:
53,517,315
Abstracts:
29,339,501
+ Search Articles
+ Subscribe to Site Feeds
EurekaMag Most Shared ContentMost Shared
EurekaMag PDF Full Text ContentPDF Full Text
+ PDF Full Text
Request PDF Full TextRequest PDF Full Text
+ Follow Us
Follow on FacebookFollow on Facebook
Follow on TwitterFollow on Twitter
Follow on Google+Follow on Google+
Follow on LinkedInFollow on LinkedIn

+ Translate

Spectrophotometric studies on alkaline isomerization of spinach ferredoxin



Spectrophotometric studies on alkaline isomerization of spinach ferredoxin



Journal of Biochemistry 98(4): 981-990



The gross protein structure, the microenvironment of the iron-sulfur cluster, and the effect of neutral salts on the molecular structure of spinach ferredoxin were studied by CD and absorption spectroscopy in the alkaline pH range. In the pH range of 7-11, the existence of reversible isomerization which consisted of at least two proton dissociation processes was indicated by the statistical CD and absorption spectra. The CD changes in the visible and far-UV regions were dramatic upon elevation of the pH from neutral to alkaline, indicating a significant alteration of the microenvironment of the cluster and a decrease in the ordered secondary structures. The absorption change in the visible region due to pH elevation was small but clearly observed with a high signal-to-noise ratio. The numbers of protons involved in the respective processes and the apparent pK values obtained from the pH-dependence of the CD changes were in good agreement with those obtained from the pH-dependence of the absorption changes in the visible region. In addition, the rate constants from the time courses of the CD and absorption changes agreed with one another. By the addition of 1 M NaCl, the CD and absorption spectra at alkaline pH were reversed almost to those at neutral pH without significant pH change. On the other hand, above pH 11, ferredoxin was found to be irreversibly denatured. Based on analyses of the statistical CD and absorption spectra and of the time courses of the CD changes, the probable mechanism of the isomerization was considered to be as follows: NH3 .**GRAPHIC**. NH2 .**GRAPHIC**. N*H2 .**GRAPHIC**. where H stands for a proton, N-form for native ferredoxin at neutral pH, N*-form for alkaline ferredoxin below pH 11 which still has the iron-sulfur cluster but with disordered secondary structures of the polypeptide chain, and D-form for completely denatured ferredoxin above pH 11. These results lead to the conclusions that (1) the interaction between the protein moiety and the iron-sulfur cluster is essential for maintaining the native ferredoxin structure, and (2) neutral salts protect the polypeptide chain from unfolding through electrostatic interaction with the ionized side chains, resulting in the stabilization of ferredoxin.

(PDF 0-2 workdays service: $29.90)

Accession: 006460757

Download citation: RISBibTeXText

PMID: 4077848



Related references

Studies on molecular structure of spinach ferredoxin by spectrophotometric methods. Iron sulfur protein research edited by Hiroshi Matsubara Yukiteru Katsube and Keishiro Wada: 0, 1987

Spectrophotometric and esr studies on the substrate interactions of ferredoxin linked nitrite reductase from spinach spinacia oleracea. Journal of Biochemistry (Tokyo) 94(6): 1833-1840, 1983

Spectrophotometric and electron spin resonance studies on the substrate interactions of ferredoxin-linked nitrite reductase from spinach. Journal of Biochemistry 94(6): 1833-1840, 1983

Alkaline isomerization of horse and yeast cytochrome c spectrophotometric and circular dichroism studies. International Journal of Peptide and Protein Research 12(5): 233-236, 1978

Ferredoxin-activated fructose diphosphatase of spinach chloroplasts. Resolution of the system, properties of the alkaline fructose diphosphatase component, and physiological significance of the ferredoxin-linked activation. Journal of Biological Chemistry 246(19): 5952-5959, 1971

Studies on spinach ferredoxin-nicotinamide adenine dinucleotide phosphate reductase. Kinetic studies on the interactions of the reductase and ferredoxin and a possible regulation of enzyme activities by ionic strength. Journal of Biological Chemistry 246(20): 6235-6241, 1971

Studies on spinach d ferredoxin nadp reductase kinetic studies on the interactions of the reductase and ferredoxin and a possible regulation of enzyme activities by ionic strength. Journal of Biological Chemistry 246(20): 6235-6241, 1971

Interactions between spinach ferredoxin and other electron carriers. The involvement of a ferredoxin:cytochrome c complex in the ferredoxin-linked cytochrome c reductase activity of ferredoxin:NADP+ oxidoreductase. Archives of Biochemistry and Biophysics 182(1): 266-272, 1977

Chemical modification of spinach ferredoxin. Properties of acetylated spinach ferredoxin. Journal of Biochemistry 81(1): 1-9, 1977

Analyses of optical absorption and circular dichroism spectra of spinach ferredoxin at alkaline pH. Journal of Biochemistry 92(4): 1049-1057, 1982