A Cross‐Linking Study of the Ca2+, Mg2+‐Activated Adenosine Triphosphatase of Escherichia coli

Abstract

The solubilized Ca²⁺, Mg²⁺‐activated adenosine triphosphatase of Escherichia coli is composed of five subunits designated α, β, γ, δ and ɛ in order of decreasing molecular weight. The subunit structure of the enzyme has been investigated by the use of the cleavable cross‐linking agents dithiobis(succinimidyl propionate), methyl‐4‐mercaptobutyrimidate, dimethyl‐3,3′‐dithiobispropion‐imidate, disuccinimidyl tartarate, and cupric 1,10‐phenanthrolinate. The products of cross‐linking were analyzed by two different two‐dimensional gel electrophoresis systems. The following cross‐linked subunit dimers were observed: α₂, β₂, αβ, αδ, βγ, βδ, βɛ and γɛ. These results, together with other published data, are discussed in relation to a model of the arrangement of the subunits in the ATPase molecule.