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. Activi ty stimulation was also observed with phosphatidylcholine, phosphatidyletha nolamine and with reductants (HSO3 and DTT). This solubilized NAD(+) kinase and the calmodulin-dependent cytosoluble isoform displayed distinct molecu lar masses, as well as different kinetic parameters. We propose that solubi lization of membrane-bound NAD(+) kinase could occur in vivo in Avena sativ a and could generate a soluble isoform.