REGULATION OF THE REDOX ORDER OF 4 HEMES BY PH IN CYTOCHROME C(3) FROM DESULFOVIBRIO-VULGARIS MIYAZAKI F

Citation
Js. Park et al., REGULATION OF THE REDOX ORDER OF 4 HEMES BY PH IN CYTOCHROME C(3) FROM DESULFOVIBRIO-VULGARIS MIYAZAKI F, Biochimica et biophysica acta. Protein structure and molecular enzymology, 1293(1), 1996, pp. 45-54
Citations number
40
Categorie Soggetti
Biology,Biophysics
ISSN journal
01674838
Volume
1293
Issue
1
Year of publication
1996
Pages
45 - 54
Database
ISI
SICI code
0167-4838(1996)1293:1<45:ROTROO>2.0.ZU;2-V
Abstract
The assignment of H-1-NMR signals of the heme methyl and propionate gr oups of cytochrome c(3) of D. vulgaris Miyazaki F was performed. The h eme assignment was revised for hemes 2 and 3 (sequential heme numberin g). Namely, heme 4 is mainly reduced at first with hemes 1, 2 and 3 fo llowing it in this order, The p(2)H titration of heme methyl signals i n four macroscopic oxidation states was performed in the p(2)H range o f 5.2 to 9.0. While the heme methyl resonances in the fully oxidized s tate showed just small changes with p(2)H, most resonances in the inte rmediate oxidation states revealed clear p(2)H dependence. In particul ar, the methyl resonances of heme 1 shifted significantly in the acidi c region. Then, the chemical shifts of beta-CH2 (next to the carboxyl group) of all propionate groups in the fully oxidized state were obser ved at various p(2)H in the range of 4.5 to 9.0. Only the propionate g roup at C-13 (IUPAC-IUB nomenclature) of heme 1 showed a clear change in this p(2)H range, its titration curve being similar to those of the methyl resonances of heme 1 in the intermediate oxidation states. pK( a) of the propionate group was 5.95 +/- 0.05. Analysis of the microsco pic formal redox potentials was carried out for the observations at p( 2)H 5.2, 7.1 and 9.0. The redox potentials of heme 1 showed the most r emarkable p(2)H dependence, resulting in the change of the order of th e redox potentials of four hemes. A significant change was also found in the interacting potential between hemes 1 and 2. In the light of th e p(2)H-titration experiments, the propionate at C-13 of heme 1 was id entified as the most plausible ionizable group responsible for the p(2 )H dependence of microscopic redox potentials of heme 1 in the acidic region.