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Published September 1990 | Published
Journal Article Open

Soluble cytochromes from the marine methanotroph Methylomonas sp. strain A4


Soluble c-type cytochromes are central to metabolism of C1 compounds in methylotrophic bacteria. In order to characterize the role of c-type cytochromes in methane-utilizing bacteria (methanotrophs), we have purified four different cytochromes, cytochromes c-554, c-553, c-552, and c-551, from the marine methanotroph Methylomonas sp. strain A4. The two major species, cytochromes c-554 and c-552, were monoheme cytochromes and accounted for 57 and 26%, respectively, of the soluble c-heme. The approximate molecular masses were 8,500 daltons (Da) (cytochrome c-554) and 14,000 Da (cytochrome c-552), and the isoelectric points were pH 6.4 and 4.7, respectively. Two possible diheme c-type cytochromes were also isolated in lesser amounts from Methylomonas sp. strain A4, cytochromes c-551 and c-553. These were 16,500 and 34,000 Da, respectively, and had isoelectric points at pH 4.75 and 4.8, respectively. Cytochrome c-551 accounted for 9% of the soluble c-heme, and cytochrome c-553 accounted for 8%. All four cytochromes differed in their oxidized versus reduced absorption maxima and their extinction coefficients. In addition, cytochromes c-554, c-552, and c-551 were shown to have different electron paramagnetic spectra and N-terminal amino acid sequences. None of the cytochromes showed significant activity with purified methanol dehydrogenase in vitro, but our data suggested that cytochrome c-552 is probably the in vivo electron acceptor for the methanol dehydrogenase.

Additional Information

© 1990 American Society for Microbiology. Received 12 April 1990; Accepted 20 June 1990. We thank A. B. Hooper, University of Minnesota, J. Lech, Medical College of Wisconsin, and B. A. Feinberg, University of Wisconsin-Milwaukee, for the use of their spectrophotometers, W. Ampholine, National ESR Center, Milwaukee, Wisc. for initial EPR spectrometric analysis, D. Teplow and J. Racs, California Institute of Technology, for amino acid analysis, and D. Teplow and H. Wong, California Institute of Technology, for N-terminal amino acid sequence. We thank A. Netrusov, Moscow State University, for preliminary activity measurements. This work was supported by a grant from the Office of Naval Research (N00014-85-K-0444-P00001).

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