Abstract
A novel enzyme "inorganic polyphosphate [poly (P) ]/ATP-NAD kinase" that utilizes both poly (P) and ATP as phosphoryl donors was purified from Micrococcus flavus. Another NAD kinase utilizing ATP, but not poly (P), was purified from Escherichia coli, and designated as "ATP-NAD kinase". The results indicated that at least two kinds of NAD kinases "poly (P) /ATP-NAD kinase" and "ATP-NAD kinase" exist in biological systems. The gene for poly (P) /ATP-NAD kinase was cloned from M. flavus (mfnk) and Mycobacterium tuberculosis H37Rv (ppnk), and that for ATP-NAD kinase was from E. coli (yfiB) and Saccharomyces cerevisiae (UTRI). Regardless of the difference of phosphoryl donor specificities, the primary structures of these NAD kinases (Mfnk, Ppnk, YfjB, and Utrlp) were highly conserved. Other than NAD kinase activity, the bacterial Mfnk and Ppnk, and yeast Utrlp showed NADH kinase activities, although YfjB did not. Furthermore, YfjB was inhibited allosterically by NADH and NADPH, suggesting that different regulation mechanisms for NAD (P) H synthesis are operating in microorganisms. Highly efficient mass production system of NADP with Ppnk was established and the system was industrialized.
