Tween-20 Activates and Solubilizes the Mitochondrial Membrane-bound, Calmodulin Dependent NAD+ Kinase of Avena sativa L.

Among different treatments assayed, a mix of a nonionic detergent (5% Tween-20) with 0.5 m NaCl was found to solubilize a large part of the calmodulin-dependent NAD⁺ kinase bound to the inner mitochondrial membrane. It also stimulated its activity by increasing 7 times the maximal velocity. Activity stimulation was also observed with phosphatidylcholine, phosphatidylethanolamine and with reductants (HSO₃ and DTT). This solubilized NAD⁺ kinase and the calmodulin-dependent cytosoluble isoform displayed distinct molecular masses, as well as different kinetic parameters. We propose that solubilization of membrane-bound NAD⁺ kinase could occur in vivo in Avena sativa and could generate a soluble isoform. Received: 6 November 2000/Revised: 18 April 2001