The Roles of c‐Type Cytochromes in Algal Photosynthesis

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Abstract
A membrane‐bound cytochrome resembling higher plant cytochrome f in many respects has been extracted from the algae Chlamydomonas, Euglena and Anacystis, and partially purified. The spectra of the cytochromes from Chlamydomonas and Euglena are virtually identical to that of parsley cytochrome f, with α‐band maxima near 554 nm, very asymmetrical β‐bands, and γ‐band maxima at 421 nm. The cytochrome from Anacystis had α and γ‐bands both shifted to slightly longer wavelengths. The redox potential of the cytochrome from Chlamydomonas was determined as +350 mV, and its minimum molecular weight in sodium dodecyl sulphate as 31000. The cytochrome from Euglena showed a rate of reaction with higher plant plastocyanin at least 100 times that of the soluble Euglena cytochrome c‐552, and was unaffected by Euglena cytochrome c‐552 antiserum. A very fast rate of electron transfer occurred between this cytochrome purified from Euglena and cytochrome c‐552. The roles of the membrane‐bound and soluble c‐type cytochromes in algal photosynthesis are discussed, and it is recommended that the name cytochrome f should be reserved for the membrane‐bound cytochrome (to emphasize its affinity with higher plant cytochrome f), while the soluble one should be named by its α‐band (c‐552, c‐553, etc.) to make clear its distinctness from higher plant cytochrome f and homology with mitochondrial cytochrome c.