Hysteretic properties of soluble F1 ATPase from Escherichia coli. Evidence for a slow transition between two conformational states of the enzyme

Laget, P.P.

Archives of Biochemistry and Biophysics 189(1): 122-131

1978


ISSN/ISBN: 0003-9861
PMID: 152094
DOI: 10.1016/0003-9861(78)90124-8
Accession: 068522430

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Abstract
The soluble E. coli coupling factor, EC .cntdot. F1 ATPase, was incubated at several temperatures ranging from -10.degree.-37.degree. C before measuring enzyme activity at 10.degree. C. Under these conditions, the specific activity strongly depends on the preincubation temperature and it appears that ATPase can be reversibly switched from a stable low-activity state to a stable high-activity state. Sedimentation experiments ruled out the possibility that this change of state was due to cold dissociation of the major subunits. Preincubation at several concentrations of protein showed that the change of state corresponded to a monomolecular reaction scheme. The curve of specific activity vs. temperature is sigmoidal, and the horizontal asymptote observed at low temperature is different from zero. Analysis of the stability of both states of the enzyme did not agree with the possibility that the low-activity state is an early intermediate of the process of cold inactivation. Experiments with enzyme missing the inhibitory subunit .epsilon., showed that this subunit is not needed for the conversion from the high-activity state to the low-activity state. The .DELTA.H values for the change of state were calculated.