The Cytochromes of Prototheca zopfii

Plant Physiol. 1970 June; 45(6): 723–727.

PMCID: PMC396501

The Cytochromes of Prototheca zopfii¹

B. L. Epel² and W. L. Butler

^aDepartment of Biology, University of California at San Diego, La Jolla, California 92037

² Present address: The Biological Laboratories, Harvard University, Cambridge, Mass. 02138.

¹ This work was supported by National Science Foundation Grant GB-6557X and a National Institutes of Health Grant GM-33,055.

This article has been cited by other articles in PMC.

Abstract

The respiratory pigments of Prototheca zopfii include seven cytochromes: two c-type cytochromes, a soluble c(549) and a membrane bound c(551); three b-type cytochromes, b(555), b(559) and b(564); and cytochromes a and a₃. Cytochromes a and a₃ could be resolved spectrally in the α-band region by reducing the cells in the presence of methanol and cyanide. Methanol shifted the absorption maximum of cytochrome a from 598 to 603 nanometers and permitted dithionite (or substrate) to reduce the cyanide-cytochrome a₃ complex to give a well defined 595-nanometer absorption band. Methanol did not interfere with CO binding by cytochrome a₃, and CO did not alter the methanol effect on cytochrome a. Azide and cyanide, which partially inhibited exogenous respiration, stimulated endogenous respiration. Frozen steady states of the electron transport chain in the presence of cyanide and azide indicated that the stimulation by these inhibitors was due to an increased autooxidation of one of the b-type cytochromes, possibly b(564).

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Selected References

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