Peculiarities of DNP-INT and DBMIB as inhibitors of the photosynthetic electron transport.

Inhibitory analysis is a useful tool for studying cytochrome b 6 f complex in the photosynthetic electron transport chain. Here, we examine the inhibitory efficiency of two widely used inhibitors of the plastoquinol oxidation in the cytochrome b 6 f complex, namely 2,4-dinitrophenyl ether of 2-iodo-4-nitrothymol (DNP-INT) and 2,5-dibromo-3-methyl-6-isopropylbenzoquinone (DBMIB). Using isolated thylakoids from pea and arabidopsis, we demonstrate that inhibitory activity of DNP-INT and DBMIB is enhanced by increasing irradiance, and this effect is due to the increase in the rate of electron transport. However, the accumulation of protons in the thylakoid lumen at low light intensity has opposite effects on the inhibitory activity of DNP-INT and DBMIB, namely increasing the activity of DNP-INT and restricting the activity of DBMIB. These results allow for the refinement of the conditions under which the use of these inhibitors leads to the complete inhibition of plastoquinol oxidation in the cytochrome b 6 f complex, thereby broadening our understanding of the operation of the cytochrome b 6 f complex under conditions of steady-state electron transport.