Evolution eukaryotic cytochromes

The resemblance among cytochrome c molecules extends to the level of amino acid sequence. Because of the molecule s relatively small size and ubiquity, the amino acid sequences of cytochrome c from more than 80 widely ranging eukaryotic species were determined by direct protein sequencing by Emil Smith, Emanuel Margoliash, and others. Comparison of these sequences revealed that 26 of 104 residues have been invariant for more than one and a half billion years of evolution. A phylogenetic tree, constructed from the amino acid sequences of cytochrome c, reveals the evolutionary relationships between many animal species (Figure 18.24). 

Nonetheless, photosynthesis did not evolve immediately at the origin of life. The failure to discover photosynthesis in the domain of Archaea implies that photosynthesis evolved exclusively in the domain of Bacteria. Eukaryotes appropriated through endosymbiosis the basic photosynthetic units that were the products of bacterial evolution. All domains of life do have electron-transport chains in common, however. As we have seen, components such as the ubiquinone-cytochrome c oxidoreductase and cytochrome hf family are present in both respiratory and photosynthetic electron-transport chains. These components were the foundations on which light-energy-capturing systems evolved. 

Gostincar C, Turk M, Gunde-Cimerman N (2010) The evolution of fatty acid desaturases and cytochrome b5 in eukaryotes. J Memb Biol 233 63-72... 

In spite of recent progress toward elucidation of the mechanism of nuclear envelope formation In modern eukaryotes, evolutionary origins of the eukaryote nucleus remain obscure. Even the concept of nuclear envelope organization around annulae derived from preexisting annulae offers little to help select among the various possibilities. Yet, similarities of Inner membrane of the nuclear envelope and the procaryotic cell membrane argue for a common parallel evolution of these two membrane types. For example, the Inner nuclear membrane Is associated with DNA (i) and perhaps even with DNA replication 21, 23) as In bacterial cells (J). There was even a report that It contained cytochrome oxidase 20), an enzyme associated with the plasma membrane of prokaryotes and critical to the development of aerobic metabolism. 

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