Preparation of two-dimensional arrays from purified beef heart cytochrome c oxidase

A method for preparing two-dimensional crystals from highly purified beef heart cytochrome c oxidase is described. This involves mixing the enzyme with phosphatidylcholine and then extracting excess lipid with deoxycholate. The reconstituted crystals show PI symmetry. Alternating rows of monomers are more closely packed (along the b axis) than in the previously described P121 crystals. However, the monomer structure in projection is the same in the two crystal forms. The P121 crystal form has been reacted with trypsin. This treatment did not alter the crystals but removed most of the impurities present in these cytochrome c oxidase preparation of low purity.