Organization of protein complexes. The component count of a protein complex is the number of different genes whose products are contained within the complex; the subunit count of a protein complex is the number of monomers within the complex (the subunit count takes into account the coefficient of each monomer within the complex; the component count does not). (A) Distribution of subunit counts for all EcoCyc protein complexes: The predominance of monomers, dimers, and tetramers is obvious—five enzymes are not included because the coefficients of their components are not known. (B) Distribution of subunit counts as a function of component counts for all complexes. In all bar diagram figures presented herein, the actual counts are shown; if the count exceeds the y-axis, it is indicated by an open face.