Stability of Isolated Chloroplast Preparations and its Effect on Hill Reaction Measurements.

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Abstract
The stability of the Hill reaction system in chloroplast preparations, as measured by the rate of dye reduction, was found to depend on the physical state of the material. Fragmented chloroplasts retained their activity longest in chloride buffer at pH 7.0 to 7.2, while intact chloroplasts retained their activity longest in glucose buffer at the same pH Chloroplasts prepared in dilute media, which were apparently intact, behaved like fragmented chloroplasts. The stability of chloroplasts prepared from 10 different plants was found to depend on species, growth conditions and on time of year (for field grown plants). The pH optimum for the storage of the Hill reaction system, 7.0 to 7.2, is different from the optimum for the reaction itself which depends on the activity of the preparation and is usually between 7.7 and 8.5. (See J. Am Chem Soc. 79, 4816, 1957). This system is very unstable at the optimum for the reaction. These results are consistent with those of other workers and resolve many of the apparent contradictions in the literature.