Figure 29.7.8.

Protein fractionation by sucrose density gradient centrifugation. Early protein fractions from the hydrophobic-interaction chromatography column are contaminated mainly with green photosystems, whereas late fractions have a significantly larger amount of phycobiliproteins. Dimeric Cyt b₆f complex forms a brown band directly above the green photosystem band. A lower-density band of monomeric Cyt b₆f complex is also observed. The dimeric Cyt b₆f complex band is harvested into multiple fractions that are further purified by sucrose density gradient centrifugation to remove residual contaminants from the neighboring bands. The purified Cyt b₆f is almost free of contaminants and is used for crystallographic studies. Figure originally published in the Journal of Biological Chemistry, Baniulis et al. (2009). For the color version, go to http://www.currentprotocols.com/protocol/ps2907.