| Abstrakt: |
2,6-dichlorophenolindophenol (DCPIP) is a redox indicator widely used to study electron transfer reactions in biological systems, including in the process of photosynthesis. DCPIP exists in solution in two forms, "pink" and "blue," which transform into each other during protonation/deprotonation. Upon reduction, the DCPIP is discolored. We investigated the pH-dependence of DCPIP reduction rate in the presence of the photosystem II (PSII) at two wavelengths: 522 nm (isobestic DCPIP point) and 600 nm (near the absorption maximum of the deprotonated "blue" form). It was shown that, in experiments with a change of the pH medium, measuring at a wavelength of 600 nm requires corrections related to changes in the ratio of the "blue" and "pink" forms of the acceptor as well as using the pK parameter of this acceptor, whose рK values vary in various sources, to calculate the DCPIP reduction rate. Measurements at the isobestic point (522 nm) allowed for avoiding these complexities. We also found that the maximum at the pH-dependence of the DCPIP reduction rate by PSII shifted by approximately 1 unit to the acidic region relative to the maximum of the acceptor pair 2,6-dichloro-p-benzoquinone–potassium ferricyanide reduction rate pH-dependence. This shift may be due to the lower availability of the QB site on the acceptor side of PSII for the charged deprotonated DCPIP form compared to the uncharged protonated form. [ABSTRACT FROM AUTHOR] |
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