Editing Cytochrome c (section)

== Species distribution ==

Cytochrome c is a highly [[conserved sequence|conserved]] protein across the spectrum of [[eukaryote|eukaryotic]] species, found in plants, animals, fungi, and many unicellular organisms. This, along with its small size (molecular weight about 12,000 [[dalton (unit)|dalton]]s),<ref name="urlCytochrome c - Homo sapiens (Human)">{{Cite web |title=Cytochrome c – Homo sapiens (Human) |url=https://www.uniprot.org/uniprot/P99999#section_seq |website=P99999 |publisher=UniProt Consortium |quote=mass is 11,749 Daltons}}</ref> makes it useful in studies of [[cladistics]].<ref name="pmid14077496">{{Cite journal |vauthors=Margoliash E |date=October 1963 |title=Primary structure and evolution of cytochrome c |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=50 |issue=4 |pages=672–9 |bibcode=1963PNAS...50..672M |doi=10.1073/pnas.50.4.672 |pmc=221244 |pmid=14077496 |doi-access=free}}</ref> Cytochrome c has been studied for the glimpse it gives into evolutionary biology.

Cytochrome c has a primary structure consisting of a chain of about 100 [[amino acid]]s. Many higher-order organisms possess a chain of 104 amino acids.<ref name="indiana">{{Cite web |title=Amino acid sequences in cytochrome c proteins from different species |url=http://www.indiana.edu/~ensiweb/lessons/molb.ws.pdf |archive-url=https://web.archive.org/web/20131228191245/http://www.indiana.edu/~ensiweb/lessons/molb.ws.pdf |archive-date=2013-12-28}}, adapted from {{cite book | vauthors = Strahler AN |title=Science and earth history: the evolution/creation controversy |date=1999 |publisher=Prometheus Books |location=Amherst, N.Y |isbn=978-1-57392-717-8 | page = 348 }}</ref> The sequence of cytochrome c in humans is identical to that of chimpanzees (our closest relatives), but differs from that of horses.<ref name="isbn978-1-4051-5089-7">{{Cite book |url=https://books.google.com/books?id=zdeWdF_NQhEC&q=chimpanzee+rhesus+cytochrome+c&pg=PA79 |title=Genes, culture, and human evolution: a synthesis |vauthors=Lurquin PF, Stone L, Cavalli-Sforza LL |publisher=Blackwell |year=2007 |isbn=978-1-4051-5089-7 |location=Oxford |page=79}}</ref>

Cytochrome c has an amino acid sequence that is highly conserved in eukaryotes, varying by only a few residues. In more than thirty species tested in one study, 34 of the 104 amino acids were conserved (identical at their characteristic position).<ref name="stryer">{{Cite book |url=https://archive.org/details/biochemistry00stry_1/page/362 |title=Biochemistry |vauthors=Stryer L |date=1975 |publisher=W.H. Freeman and Company |isbn=978-0-7167-0174-3 |edition=1st |location=San Francisco |page=[https://archive.org/details/biochemistry00stry_1/page/362 362] |url-access=registration}}</ref>  For example, human [[cytochrome oxidase]] reacted with wheat cytochrome ''c'', ''in vitro''; which held true for all pairs of species tested.<ref name="stryer" /> In addition, the redox potential of +0.25 volts is the same in all cytochrome ''c'' molecules studied.<ref name="stryer" />