. Thus the reaction of nucleoside diphosphate kinases can be generalized as follows: NDP + ATP ´ NTP + ADP. The activity of NDPK is very high in most organisms including plants (Hirose and Ashihara, 1984), and the equilibrium constant is almost unity. NDPK activ- ity is not known to be regulated by any allosteric effectors In addition to NDPK’s primary role as a catalyst, many other biological phenomena appear to rely on NDPK activ- ities.