Properties of Rat Brain Nad‐kinase

NAD‐kinase was purified from rat brain acetone powder according to the method of Wang and Kaplan (1954). The acetate buffer supernatant showed only very low specific activity but was largely free of the factors that interfere with the enzyme assay. The Michaelis constants for both substrates were determined, the values were 0·5 mm for NAD and 4·0 mm for ATP. The optimal pH was 7·4 in tris‐HCl buffer and the highest NAD‐kinase activity was observed in the hyaloplasm fraction. NADH2 inhibited the enzyme whereas NADPH2 did not. Finally, the reversible inhibition of SH‐binding compounds is described and the observed properties of rat brain NAD‐kinase compared with the properties of NADP synthesizing enzymes from pigeon liver and rat liver.