Behavior of fragmented calcium (II) adenosine triphosphatase from sarcoplasmic reticulum in detergent solution

The behavior of Ca2+-ATPase from sarcoplasmic reticulum in detergent solution was compared with that of Ca2+-ATPase which had been cleaved in half by limited trypsin digestion. Attempts to dissociate the fragments (I and II) with an excess of detergent micelles demonstrated that fragments I and II are structurally dependent upon each other, and that they must be denatured in order to be dissociated. Partial dissociation of the fragmented ATPase was found to occur in the bile salt detergents, deoxycholate and cholate, and optical data showed that there was an accompanying change in conformation. No dissociation of the fragmented ATPase was observed in nonionic detergents. The fragmented ATPase retained the same specific activity and stability as the intact ATPase under a variety of conditions when solubilized in Tween 80 or dodecyl octaoxyethylene glycol monoether. The data demonstrate that the noncovalent interactions that maintain the native conformation of the ATPase are not affected by either trypsin cleavage or solubilization in nonionic detergent solution.