Interaction of electron acceptors with thylakoids from halophytic and non-halophytic species

Abstract

Thylakoid membranes isolated from halophytic species showed differences in their interactions with ionic and lipophilic electron acceptors when compared to thylakoids from non-halophytes. FeCN was considerably less efficient as electron acceptor with halophyte thylakoids, supporting much lower rates of O2 evolution and having a lower affinity. FeCN accepted electrons at a different, DMMIB insensitive, site with these thylakoids. 1,4-Benzo-quinones with less positive midpoint potentials were less effective in accepting electrons from halophyte thylakoids compared to nonhalophyte thylakoids, also reflected in lower rates of O2 evolution and lower affinity. Considering the lipolphilic nature and the fact that there was no apparent change in the site donating electrons to the quinones, an alteration in the midpoint potential of this site by about +100mV is postulated for the halophyte thylakoids.

Investigation of photocurrents resulting from a living unicellular algae suspension with quinones over time

“…The differences in quinones can largely be summarized by electrophilicity. Taking PPBQ, DCBQs and 2,6-DMBQ as examples and the midpoint potentials (Q/QH 2 ) at pH 7 that have been reported in the literature ( Scheme 1 ), 37 , 51 , 52 we can find a general trend in electrophilicity according to a higher E °′ value: 53 DCBQs, PPBQ, and DMBQ (from highest to lowest). Thus, DCBQs are more able to react with nucleophiles than PPBQ, which exhibits better partitioning into membranes and may quench chlorophylls directly (because this phenomenon occurs within membranes, i.e.…”

Control of misses in oxygen evolution by the oxido-reduction state of plastoquinone in Dunaliella tertiolecta

“…In halophytic algae, benzoquinone accepts electrons from the plastoquinone pool and from a site near QB (Preston and Critchley 1988). In Fig.…”

The Cytochrome b6f Complex Is Not Involved in Cyanobacterial State Transitions

“…They based their proposal on the results obtained by chemically inducing state transitions in Synechocystis and Synechococcus PCC 7002 using 2,6-dimethoxy-1,4-benzoquinone (DMBQ), p-benzoquinone (PBQ), and 2,5-dibromo-3methyl-6-isopropyl-p-benzoquinone (DBMIB). DMBQ and PBQ accept electrons from the PQ pool (Preston and Critchley, 1988), while DBMIB inhibits cyt b 6 f activity by attaching to the Qo site (the PQH 2 binding site), preventing reoxidation of the PQ pool (Roberts and Kramer, 2001; Figure 6). These authors found that the addition of DMBQ (or PBQ) to dark-adapted cells induced an increase in F md , which they attributed to a partial transition to State I triggered by oxidation of the PQ pool.…”