Substrate water exchange in photosystem II depends on the peripheral proteins
Date
2001
Authors
Hillier, Warwick
Hendry, G
Burnap, Robert L
Wydrzynski, Thomas
Journal Title
Journal ISSN
Volume Title
Publisher
American Society for Biochemistry and Molecular Biology Inc
Abstract
The 18O exchange rates for the substrate water bound in the S3 state were determined in different photosystem II sample types using time-resolved mass spectrometry. The samples included thylakoid membranes, salt-washed Triton X-100-prepared membrane fragments, and purified core complexes from spinach and cyanobacteria. For each sample type, two kinetically distinct isotopic exchange rates could be resolved, indicating that the biphasic exchange behavior for the substrate water is inherent to the O 2-evolving catalytic site in the S3 state. However, the fast phase of exchange became somewhat slower (by a factor of ∼2) in NaCl-washed membrane fragments and core complexes from spinach in which the 16- and 23-kDa extrinsic proteins have been removed, compared with the corresponding rate for the intact samples. For CaCl2-washed membrane fragments in which the 33-kDa manganese stabilizing protein (MSP) has also been removed, the fast phase of exchange slowed down even further (by a factor of ∼3). Interestingly, the slow phase of exchange was little affected in the samples from spinach. For core complexes prepared from Synechocystis PCC 6803 and Synechococcus elongatus, the fast and slow exchange rates were variously affected. Nevertheless, within the experimental error, nearly the same exchange rates were measured for thylakoid samples made from wild type and an MSP-lacking mutant of Synechocystis PCC 6803. This result could indicate that the MSP has a slightly different function in eukaryotic organisms compared with prokaryotic organisms. In all samples, however, the differences in the exchange rates are relatively small. Such small differences are unlikely to arise from major changes in the metal-ligand structure at the catalytic site. Rather, the observed differences may reflect subtle long range effects in which the exchange reaction coordinates become slightly altered. We discuss the results in terms of solvent penetration into photosystem II and the regional dielectric around the catalytic site.
Description
Keywords
Keywords: Bacteria; Biological membranes; Calcium compounds; Mass spectrometry; Oxygen; Substrates; Water; Catalytic sites; Proteins; ligand; manganese stabilizing protein; metal; oxygen 18; protein; triton x 100; unclassified drug; water; Mn stabilizing protein; M
Citation
Collections
Source
Journal of Biological Chemistry
Type
Journal article
Book Title
Entity type
Access Statement
License Rights
Restricted until
2037-12-31
Downloads
File
Description