Activation Parameters of the Adenosine Triphosphatase of Micrococcus lysodeikticus A Comparison of the Soluble and Membrane‐Bound Forms of the Enzyme

Abstract
The Arrhenius plots for the membrane-bound ATPase and its soluble form purified from M. lysodeikticus, presented discontinuities near 30.degree. C at pH 7.5. Glycerol-containing lipids were not responsible for these discontinuities. The values of the enthalpies of activation were 12(soluble) and 22 (membrane-bound) kcal/mol (50.2 and 92.0 Kj/mol) above 30.degree. C and 42 (soluble) and 29 (membrane-bound) kcal/mol (175.7 and 121. 3 Kj/mol) below that temperature. Both molecular forms of the ATPase were apparently able to adopt at least 2 different structures, above and below the critical temperature. Of the 2, only the high-temperature structure seemed to be enzymically active. In the case of lipid-dependent ATPases, such as the Escherichia coli enzyme, the transition between both enzyme structures probably occurred with simultaneous melting of their lipid microenvironment.

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