Journals of Gerontology Series A: Biological Sciences and Medical Sciences, Vol 52, Issue 5 B240-B244, Copyright © 1997 by The Gerontological Society of America
The stable, inactive but reactivatable, unfolding intermediate of rat muscle sarcoplasmic reticulum Ca(2+)-ATPase differs from the age- modified form of this protein
NC Bergenhem, SJ Lee and A Gafni
Department of Biological Chemistry, University of Michigan, USA.
Ca(2+)-ATPase from rat skeletal-muscle sarcoplasmic-reticulum has been
reported to be less stable in old animals. These changes were suggested to
be due to age-related modifications in the membrane. In the present study,
the guanidinium-chloride (GuHCl)-induced inactivation, and reactivation by
dilution of the denaturant, of this enzyme have been investigated. The
cooperativity of the inactivation-transition was found to increase when the
membrane was dissolved in the non-ionic detergent polyoxyethylene 10
laurylether. There is an inactive unfolding intermediate in equilibrium
with the native state at low concentrations of GuHCl. This intermediate can
be reactivated, even after as long a time as 19 h. The stability of this
intermediate is only slightly affected by detergent solubilization of the
enzyme. Hence, the membrane probably only plays a minor role in stabilizing
the intermediate.
