Frank Müh, M. Bibikova, Eberhard Schlodder, D. Osterhelt, W. Lubitz,
"Conformational relaxation following reduction of the photoactive bacteriopheophytin in reaction centers from Blastochloris viridis. Influence of mutations at position M208"
, in Elsevier Science BV, in BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS, Vol. 1459, Nummer 1, 7-2000, ISSN: 0005-2728
Conformational relaxation following reduction of the photoactive bacteriopheophytin in reaction centers from Blastochloris viridis. Influence of mutations at position M208
Sprache des Titels:
The photochemically trapped bacteriopheophytin (BPh) b radical anion in the active branch (Phi(A)(.-)) of reaction centers (RCs) from Blastochloris (formerly called Rhodopseudomonas) viridis is characterized by H-1-ENDOR as well as optical absorption spectroscopy. The two site-directed mutants YF(M208) and YL(M208), in which tyrosine at position M208 is replaced by phenylalanine and leucine, respectively, are investigated and compared with the wild type. The residue at M208 is in close proximity to the primary electron donor, P, the monomeric bacteriochlorophyll (BChl), B-A, and the BPh, Phi(A), that are involved in the transmembrane electron transfer to the quinone, Q(A), in the RC. The analysis of the ENDOR spectra of Phi(A)(.-) at 160 K indicates that two distinct states of Phi(A)(.-) are present in the wild type and the mutant YF(M208), Based on a comparison with Phi(.)(A-) in RCs of Rhodobacter sphaeroides the two states are interpreted as torsional isomers of the 3-acetyl group of Phi(A). Only one Phi(A)(.) state occurs in the mutant YL(M208). This effect of the leucine residue at position M208 is explained by steric hindrance that locks the acetyl group in one specific position. On the basis of these results, an interpretation of the optical absorption difference spectrum of the state Phi(A)(.-)Phi(A)(.-) is attempted. This state can be accumulated at 100 K and undergoes an irreversible change between 100 and 200 K [Tiede et al., Biochim. Biophys. Acta 892 (1987) 294-302]. The corresponding absorbance changes in the BChl Q(x) and Q(y) regions observed in the wild type also occur in the YF(M208) mutant but not in YL(M208). The observed changes in ...