Cooperativity of the αβ ‐protomer structure in Na+, K+‐ATPase functioning

[摘要]

Heat denaturation of the free and ligand-bound forms of purified Na⁺,K⁺-ATPase from pig kidney is studied with the scanning microcalorimetry technique. A single two-state transition is observed during denaturation of the free enzyme, the molar concentration of the cooperatively melting units being equal to the concentration of αβ-protomers (M _r≈140000). Upon interaction of the enzyme with phosphate, Mg²⁺, and strophanthidin, but not with Na⁺, the cooperativity of the protomer unfolding is lost, and the protein stabilization enthalpy becomes ≈ 230 higher. The data suggest that (i) in a functionally active enzyme form, the αβ-protomers possess a rigid structure with tight association of their subunits and domains, (ii) this structural rigidity is essential for the Na⁺,K⁺-ATPase functioning and (iii) there is a unique non-active conformation of the enzyme which may play an important role in its in vivo regulation.

[学科分类] 生物化学/生物物理

[关键词] Na +;K+-ATPase αβ-Protomer Structure cooperativity Enzyme conformation Scanning microcalorimetry