[Quaternary structure of NAD-kinase from rabbit liver]

A procedure for isolation of NAD-kinase from rabbit liver resulting in 4000-fold purification and the activity yield of 50-60% is described. The molecular weight of the NAD-kinase subunit determined by SDS electrophoresis is 30 000. The purified enzyme is a dimer. Partially purified preparations of NAD kinase contain multiple forms with mol. Weights ranging from 650 000 to 180 000 and have complex kinetic behaviour. A thermostable activator of NAD-kinase which, when added to the homogeneous enzyme preparation, destroys the linear dependence of the enzyme specific activity on concentration, was detected. The nature of multiple forms of NAD-kinase and the possible role of the activator in their formation is discussed.