Light-induced absorbance changes in Fraction I particles prepared from spinach chloroplasts by French-press treatment

Light-induced changes of absorbance were measured in Fraction 1 particles prepared from spinach chloroplasts according to a method developed by

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⁶ that employs breakage of chloroplasts in the French pressure cell and centrifugation of the resulting fragments on a sucrose density gradient. Absorbance changes were measured in the presence of ascorbate and 2,3,5,6-tetramethyl-1,4-phenylenediamine as an electron donating system. In addition to the oxidation of P₇₀₀ and cytochrome f, that was investigated in our previous study¹¹, three other light-induced absorbance changes were observed; reduction of cytochrome b with a peak at 562 nm, the so-called 515-nm change showing an absorbance increase at 515 nm and a decrease at 480 nm, and a broad band of unknown absorbance increase covering wave-lengths from 490 to 570 nm. Uncouplers such as carbonylcyanide-m-chlorophenylhydrazone and gramicidin D inhibited the 515-nm change under continuous light and accelerated the dark decay of flash-light-induced change. The other broad absorbance change was insensitive to these inhibitors.