For all enzymes showing phosphorylating activity towards nucleosides or nucleotides working pH ranges were determined, except for TmTK, TmPK, TmAcK and TmPPDK. For the latter enzymes, the optimal reaction pH has already been described ( , Table ). Working pH ranges differed depending on the enzyme classes. While TmPK and TmAcK preferred a lower reaction pH, TmTK, TmRK and nearly all TmNMPKs (except for Tm(d)CMPK) showed a comparable activity in a pH range of 7 to 9 (Table , Figure ). [a] The working pH ranges were determined by comparing specific activities (Figure ). Reactions with 2 mM MgCl2, 5 mM DTT, 50 mM KCl, 1 mM substrate (AMPK: dAMP, (d)CMPK: CMP, GMPK: GMP, RK: Urd, TMPK: TMP, UMPK: UMP) and 1.2 mM ATP in 70 mM Tris-HCl (pH 7, 8, 9) were preheated to 37 °C. Reactions were started with appropriate enzyme dilutions. Samples were stopped after 5 min incubation with cold deionized water and were analyzed by the luminescent assay. [b] optimal pH