Photosynthesis by Isolated Chloroplasts IX. Photosynthetic Phosphorylation and CO2 Assimilation in Different Species

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Abstract
Until recently the only experimentally documented photochemical activity of isolated chloroplasts was the Hill reaction. In the last 5 years, work with isolated spinach chloroplasts has demonstrated their capacity for carrying out 3 new basic reactions: non-cyclic photophosphorylation (Equation 1), cyclic photophosphorylation (Equation 2) and CO2 assimilation to the level of carbohydrates (Equation 3). CO2 assimilation in Reaction 3 is driven by the "assimi-latory power", i.e. reduced triphosphopyridine nucleotide (TPNH2) formed by Reaction 1 and by adenosine triphosphate (ATP) formed by Reactions 1 and 2.[image].In a non-physiological variant of Reaction 1, TPN is replaceable by ferricyanide (Equation 4):.[image].The authors consider the Hill reaction to be a fragment of Reaction 4 in which electron transport (measured here by ferricyanide reduction) is uncoupled from a normally concurrent phosphorylation. Because of the importance of Reactions 1, 2, 3 and 4 to the understanding of the mechanism of photosynthesis these have been investigated and found to be present in chloroplasts isolated from 4 species other than spinach: sugar beet, sunflower, pokeweed, and Tetragonia expansa.