Photosystem II is an ancient protein that is currently believed to have been first used by cyanobacteria. The exact mechanism in which this protein elvolved is poorly understood. One area of reserach that has been particularily interesting is the possesion of both PS I (Photosystem I) and PS II. It is accepted that PS I was the first of the two systems to evolve because of its resemblance to bacteria chlorophyll which functioned in an anoxygenic enviroment.

The leading theory is that there was a gene duplication during the evolutionary path of PS I and in to PS II


Below is an image of an alignment in PyMol of the a-chains of PS II from Thermosynechococcus elongatus(1S5L, in yellow) and Thermosynechococcus vulcanus (3ARC, in red)

Alignmet with lable

This image shows the cartoon representations of two a-chain's of the PS II proteins of Thermosynechococcus elongatus (yellow) and Thermosynechococcus vulcanus (red) superimposed on each other. The alignment rmsd (root mean square deviation) equals 0.536 Angstroms


  1. Rogelio: Photosystem II: Introduction
  2. Rogelio: Photosystem II: Biological function
  3. Rogelio: Photosystem II: Biosynthesis
  4. Rogelio: Photosystem II: Gene sequence
  5. Rogelio: Photosystem II: Amino acid sequence and composition
  6. Rogelio: Photosystem II: Secondary and tertiary structure
  7. Rogelio: Photosystem II: Domains and structural motifs
  8. Rogelio: Photosystem II: Interactions with macromolecules and small molecules
  9. Rogelio: Photosystem II: Molecular biodiversity and evolution
  10. Rogelio: Photosystem II: Literature overview
  11. Rogelio: Photosystem II: Useful online resources