Photosynthetic reaction center (1PRC) - This large protein resides in the plasma membrane of the bacterium Rhodopseudomonas viridis where it absorbs light and uses that energy to pump protons across the membrane up their concentration gradient. The protons then move back across the membrane (down their concentration gradient) through a different protein that phosphorylates ADP to make ATP. The ATP can then be used for various biosynthetic reactions.

Notice that this protein is composed of 4 subunits, two of which are mostly within the membrane (light blue and green) and are almost entirely composed of membrane-spanning alpha helices. This is a side view along the plane of the membrane. The other two subunits (dark blue and yellow) extend away from the membrane. What types of amino acid R-groups (hydrophilic or hydrophobic) would most likely be sticking out from the membrane spanning subunits? (Hint - What do they interact with?)

8/22/04 Copyright (C) 2004, Jonathan Monroe, monroejd@jmu.edu. All rights reserved.
URL: http://csm.jmu.edu/biology/courses/bio220/photorc.html