Measurable levels of activity of NAD+ kinases of actinomycetes Micrococcus luteus and Corynebacterium ammoniagenes were observed after substituting inorganic tripolyphosphate for ATP, whereas the enzyme from the eubacterium Escherichia coli was not active with this substrate. Gradient PAGE found two molecular isoforms of NAD+ kinase in C. ammoniagenes and E. coli; four forms were found in M. luteus. All isoforms of this enzyme found in C. ammoniagenes and M. luteus displayed a NADP-synthesizing activity in the presence of either ATP or tripolyphosphate. Because of its capability of utilizing inorganic tripolyphosphate, M. luteus is the most promising NADP producer organism.