ELECTROGENICITY OF ELECTRON AND PROTON-TRANSFER AT THE OXIDIZING SIDEOF PHOTOSYSTEM-II

Citation
M. Haumann et al., ELECTROGENICITY OF ELECTRON AND PROTON-TRANSFER AT THE OXIDIZING SIDEOF PHOTOSYSTEM-II, Biochemistry, 36(31), 1997, pp. 9304-9315
Citations number
79
Categorie Soggetti
Biology
Journal title
ISSN journal
00062960
Volume
36
Issue
31
Year of publication
1997
Pages
9304 - 9315
Database
ISI
SICI code
0006-2960(1997)36:31<9304:EOEAPA>2.0.ZU;2-A
Abstract
The electrogenicity of electron and proton transfer at the oxidizing s ide of PSII was monitored by transmembrane electrochromism of caroteno ids in thylakoids and, independently, by electrometry in oxygen-evolvi ng photosystem II core particles. It yielded dielectrically weighted d istances between cofactors, They were related to the one between Y-Z(o x) and Q(A)(-) (=100%). The electron transfer from Y-Z to P-680(+) ran ged over a relative distance of 15%, while the one from Mn-4 to Y-Z(ox ) ranged over less than 3.5%. The latter result placed Mn-4 and Y-Z at about the same weighted depth in the membrane. The oxidation of cofac tor X by Y-Z(ox) during S-2 --> S-3 ranged over 10%. We tentatively at tributed 7% to proton transfer into the lumen and 3% to electron trans fer, in line with our notion that one proton is liberated from X-ox it self. This placed X at the same depth in the membrane as Mn. Proton re lease upon the final oxidation of water during the oxygen-evolving ste p S-4 --> S-0 revealed relative electrogenic components of 5.5% in car e particles and between 10.5% (pH 7.4) and 2% (pH 6.2) in thylakoids. The former likely reflected proton transfer from bound water into the lumen and the latter to intraprotein bases that were created in the fo regoing transitions, A tentative scheme for the arrangement of cofacto rs al the oxidizing side of photosystem II is presented.