Elucidating the Light Reactions (1950–1961)
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The final chapter looks at how the “light” reactions in photosynthesis were elucidated in the 1950s. This pursuit culminated in the two-photoreaction, two-pigment system model, which still dominates the field. Three strands of research are identified that led to this model: (1) the investigation of how reducing power (today: nicotinamide adenine dinucleotide phosphate (NADP)) was synthesised; (2) the discovery of photophosphorylation, that is, the production of adenosine triphosphate (ATP), in plant cells; (3) the search for a photosynthetic electron transport chain. The development of new spectroscopic methods was highly important in this context, since, for the very first time, it became possible to nail down the changing redox states of individual molecules. It was also in this period that photosynthesis researchers first tried to localise the partial processes in the cellular environment. And they experimented with various forms of graphs to visualise the mechanism. In contrast to the study of the carbon reduction process, analysed in Chap. 6, several research teams independently worked on this question, and almost simultaneously came to very similar conclusions; major players including Louis N. M. Duysens, Bessel Kok, Robin Hill and Horst T. Witt. The convergence of their results, although they had very different starting points and methodologies, was enormously persuasive. The model subsequently became known as the “Z-scheme” (after a standard form of representation), and this is how it features in textbooks of the field to this day.