Plant Nucleotide Metabolism. Hiroshi Ashihara

7.0–7.5 1.5 300 Guranowski (1979b) Peach flower buds^a) 9.5 1.8 200 Faye and Le Floc'h (1997) Tobacco BY-2 cells^a) Laukens et al. (2003) Arabidopsis thaliana ^b) ADK1 8.0 0.5 350 3.2 adk1 AT3G09820 Moffatt et al. (2000) ADK2 9.5 0.3 370 4.8 adk2 AT5G03300 Tobacco BY-2 cells^b) ADK1T 7.5 4.0 2.4 0.3 3.9 adk1t Kwade et al. (2005) ADK1S 7.0 1.9 2.5 6.1 3.9 adk1s ADK2T 8.5 7.3 3.2 8.7 2.6 adk2t ADK2S 8.8 3.9 2.2 1.7 3.8 adk2s Physcomitrella (moss)^{b) c)} von Schwartzenberg et al. (1998) IGK IR GR XR ATP Jerusalem artichoke^a) 7.6 70 14 1450 Combés et al. (1989) dNK AdR GdR A. thaliana ^b) 14 27 dnk AT1G72040 Clausen et al. (2012)

      AR, Adenosine; ATP, adenosine triphosphate. Cytokinin ribosides: DHZR, dihydrozeatin riboside; iPR, isopentenyladenosine; tZR, trans-zeatin riboside. IR, Inosine; GR, guanosine; XR, xanthosine; AdR, deoxyadenosine; GdR, deoxyguanosine.

      a) Native enzyme.

      b) Recombinant enzyme.

      c) Activity was detected but no data was published on the Km value.

Almost homogeneous AK was isolated from seeds of yellow lupin (Lupinus luteus) by Guranowski (1979b). The Km value for adenosine was low (1.5 μM), but was higher (300 μM) for ATP. This trend is also found with AK from other plant sources (Table 5.3). ATP is the main phosphate donor. dATP and guanosine