Enzymatic kinetics of photosystem II with DCBQ as a substrate in extended Michaelis-Menten model

• Published in: Journal of photochemistry and photobiology. B, Biology Vol. 247; p. 112780
• Main Authors: Paweł, Rogowski, Aleksandra, Urban, Elżbieta, Romanowska
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.10.2023
• Subjects: Chloroplast; Enzyme kinetics; Mathematical modeling; Oxidation-reduction (redox); Photosystem II; Plastoquinone; Quasi-steady state approximation; LL; HL; Chl; PSII; PQ-9; Photosystem II; K; M-M; M; RPM; KmA,KmB; BS; DCBQ; HTG-PSII; QSSA; Chloroplast; YZ; Plastoquinone; e; VmA,VmB; Quasi-steady state approximation; EDTA; PVDF; ES; Tris; SDS-PAGE; LHCII; Oxidation-reduction (redox); Mathematical modeling; HTG; MES; Enzyme kinetics
• ISSN: 1011-1344; 1873-2682
• DOI: 10.1016/j.jphotobiol.2023.112780

This study aimed to examine enzymatic kinetics of photosystem II (PSII) of maize mesophyll chloroplasts using the artificial electron acceptor 2,6-dichloro-1,4-benzoquinone (DCBQ) as a substrate. We extended Michealis–Menten kinetics model assuming that DCBQ can accept electrons from PSII in two ways: from a QB directly or from QA by docking in the QB site. We used a Clark oxygen electrode for measuring the PSII activity, depending on the concentration of DCBQ. We found that: [1] DCBQ acts as an electron acceptor or [2] as an inhibitor for PSII. At a concentration < 0.2 mM, DCBQ accepted electrons from the QB at a rate of 889 electrons/s, while at >> 0.2 mM it replaced QB following which the activity decreased to zero. DCBQ located in the QB also increased the affinity of the substrate to PSII. We determined the kinetic parameters for the chloroplasts of plants growing under high and low light intensity, to change thylakoid stacking and thus the rate of electron transport. The parameter KmB, which is a measure of the affinity of DCBQ to PSII, showed quantitative changes based on light intensity, while K was proportional to the size of the plastoquinone pool. We believe that our model can be applied as a tool to study “State transitions” and induced changes in grana stacking in plants exposed to various stresses, which will facilitate the regulation of electron transfer pathways through an appropriate balance between linear and cyclic electron transport. •We extended Michaelis–Menten model which describes the enzymatic kinetics of PSII in light-saturated conditions.•Low concentration DCBQ acts as an electron acceptor for PSII, while at high concentrations it inhibits this enzyme.•KmB constant is measure of DCBQ affinity to PSII and its value is proportional to the degree of grana stacking in chloroplasts.•K constant correlates with the content of the plastoquinone pool, was lower for chloroplasts of low-light-grown plants.