Cytochrome c Cytochrome c is a small alpha-helical protein that contains one heme group. The water molecules are shown as red spheres, except one in green. The green one is an example of a water molecule that is found within the protein structure. Most of the water molecules are on the surface. Takano, T., Dickerson, R. E.: Redox conformation changes in refined tuna cytochrome c. Proc Natl Acad Sci U S A 77 pp. 6371 (1980) (Pubmed) 3cyt (PBD)