PH-METRIC STUDY OF REACTION CENTERS FROM PHOTOSYNTHETIC BACTERIA IN MICELLULAR SOLUTIONS - PROTONATABLE GROUPS EQUILIBRATE WITH THE AQUEOUSBULK PHASE

Citation
L. Kalman et al., PH-METRIC STUDY OF REACTION CENTERS FROM PHOTOSYNTHETIC BACTERIA IN MICELLULAR SOLUTIONS - PROTONATABLE GROUPS EQUILIBRATE WITH THE AQUEOUSBULK PHASE, Biochemistry, 36(15), 1997, pp. 4489-4496
Citations number
43
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Biology
Journal title
ISSN journal
0006-2960
Volume
36
Issue
15
Year of publication
1997
Pages
4489 - 4496
Database
ISI
SICI code
0006-2960(1997)36:15<4489:PSORCF>2.0.ZU;2-A
Abstract
Hydrogen ion equilibria of the reaction center protein from photosynth etic purple bacteria Rhodobacter sphaeroides and Rhodobacter capsulatu s dissolved in micellular solution were studied by acid-base titration to estimate the water accessibility of protonatable residues of the p rotein determined from structural data. The ionizable amino acids of t he reaction center underwent protonation - deprotonation with protons from the interfacial layer, which, however, exchanged protons from the aqueous bulk phase. The equilibrium was described in terms of the buf fering capacity of the multiphase system. The detergents decreased the proton activity coefficient (increased the buffering capacity) of the aqueous solution by a factor of 0.33 (in 0.03% Triton X-100 and LDAO) and 0.12 (0.04% dodecyl beta-D-maltoside). The observed buffering cap acities of the reaction center protein were large and detergent-depend ent. However, corrections for proton activities made the pH dependence of buffering capacities in different detergents uniform and similar t o that expected from the number and pK values of protonatable groups o f the protein. The vast majority of protonatable amino acids of the re action center are in protonation equilibria with the aqueous bulk phas e on an extended time scale.