As other enzyme classes like nucleotidases and family B 6-phosphofructokinases (PfkB) are also known for the phosphorylation of nucleotides, they were also included in this study. Indeed, the KEGG pathway for the purine nucleotide metabolism suggests that the 5'/3'nucleotidase SurE (TmNuc) of T. maritima might catalyze the formation of purine NMPs (Figure ) which led us to integrate this enzyme into our study. Additionally, the T. maritima genome encodes for 6 enzymes of the PfkB-family including a ribokinase . Ribokinase of T. maritima was described to show a high structural similarity to the nucleoside kinase of Methanocaldococcus janaschii which accepted all natural ribonucleosides . Therefore, the ribokinase of T. maritima was selected in this study to evaluate whether it can accept nucleosides as substrates. Other PfkBfamily enzymes were excluded from this study as they were shown before to be very specific for their sugar substrate .