1. Ethanol-extracted spinach chloroplasts were carefully sonified in a mixture of buffered urea, TRITON X-100 and dithiothreitol. This procedure solubilized the membrane-bound b-type cytochromes 559 and 563 to approx 90%. The crude extract contained both the high-potential (HP) and the low-potential form (LP) of cytochrome b-559 in a molar ratio of 1:1.
2. Strong sonification doubled the amount of low potential cytochrome b-559 in the extract. Therefore, it is assumed that Cyt b-559 HP was completely converted into the low-potential form.
3. Cyt b-563 was solubilized in the same concentration by both methods.
4. In the same medium (see No. 1), cytochrome f (= Cyt c-554) was dissolved by strong sonification only and is then essentially present in the extract in a dithionite-reducible form.
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