Characteristics of DDT-Sensitive Ca-ATPase in the Axonic Membrane

Abstract

A highly DDT-sensitive Ca-ATPase was found in an axonic nerve preparation from the lobster legs. As a result of several attempts to isolate the enzyme apart from other ATPases, an assay condition was devised. This method gives rise to the ATPases activity which is totally sensitive to DDT. By using such an approach the characteristics of the Ca-ATPase was studied. The 150 of the enzyme toward DDT was found to be in the neighborhood of 10⁻⁹ M. It has a rather high Ca⁺⁺ optimum (0.3 mM) suggesting that it is likely an ecto Ca-ATPase located at the surface of the axons. This was confirmed by using an axonic suspension preparation which gave essentially identical results on Ca-ATPase activities and its characteristics. The inhibition of the Ca-ATPase appears to result in the suppression of Ca⁺⁺ uptake process at the surface of the membrane as judged by a ⁴⁵Ca⁺⁺ uptake experiment by using both the membrane and the axonic suspension preparations in the presence of ATP. These results help to explain why DDT poisoned nerve membranes are prone to destabilization and subsequent excitation.

A major portion of the experiment presented in this manuscript was conducted in the Department of Entomology, University of Wisconsin — Madison.