Calmodulin dependent NAD-kinase is associated with both the outer and inner mitochondrial membranes in maize roots.
Maize root mitochondrial have been subfractionated after osmotic rupture. A calcium-calmodulin-dependent NAD-kinase activity has been shown to be present in both inner and outer membrane fractions. Cytochrome c-reductase activities are also associated with outer and inner membrane fractions but whereas the former is entirely insensitive to 50 μmol·1(-1) antimycin A the latter is reduced by 60% in its presence. This residual antimycin A-insensitive cytochrome c-reductase activity cosediments with the major portion of NAD-kinase activity and equilibrates in sucrose gradients at densities around 1.146 g·cm(-3). Rate zonal centrifugation with renografin allows an excellent separation of both cytochrome c-reductase and NAD-kinase activities. We have no evidence for allocating NAD-kinase activity to endo- or plasma membranes.
Abteilung Cytologie des Pflanzenphysiologischen Instituts der Universität Göttingen, Untere Karspüle 2, D-3400, Göttingen, Federal Republic of Germany.
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Sauer
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Robinson