THERMAL INACTIVATION OF RABBIT LIVER NAD-KINASE

Thermal inactivation of homogenous NAD-kinase and of its partially pur ified preparation containing NAD-kinase complexed with glutamate dehyd rogenase has been studied. The complex is more thermostable than the i solated NAD-kinase; its inactivation proceeds through irreversible dis sociation following a period of constant activity. No period of consta nt activity is observed during thermal inactivation of homogenous NAD- kinase, which is a two-step process: in the first step tetramers rever sibly dissociate into dimers, and in the second step the dimers are ir reversibly denatured. The activation energies for dissociation and den aturation are 40 and 52 kcal/mole, respectively.