Light and dark rate-determining steps in electron transport reactions in spinach chloroplasts

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Effects of various factors, such as uncouplers, inhibitors and inhibitory treatments of chloroplasts , on light-dependent (K_L) and -independent (K_D) Parameters estimated from the light intensity-activity relationship, were studied. In the Hill reaction with ferricyanide or methyl viologen as electron acceptor, a reagent or treatment affecting electron transport on one side of system II, which included the rate-limiting step for the entire electron transport, affected only K_D. In contrast, a change in the rate of electron transfer on the other side of system II affected only K_L. We inferred that K_D represents the rate of the dark rate-limiting step at infinite light intensity. On the other hand, K_L is concerned to the quantum yield of the primary reaction, as well as to the rate constant of the reaction on the side of system II opposite to that of the rate-limiting step at infinite light intensity. Effects of inhibitors and treatments on the reaction parameters changed markedly depending on the pH of the reaction medium. However, the contrasting effects of inhibitors affecting the opposite sides of system II were consistently observed in defined levels of pH. This was also the case in the photoreduction of methyl viologen with the ascorbate-DPIP couple as electron donor.
日本植物生理学会の論文