The conversion of NDPs to NTPs usually is catalyzed by wide-spectrum NDPKs. Surprisingly, the genome of T. maritima does not encode for a NDPK. Therefore, we included enzymes capable of performing a similar function as NDPKs in this study. We focused on enzymes widely used for ATP regeneration as they are well known to catalyze NTP formation. Furthermore, it was shown that pyruvate kinase is a candidate for a PEP-dependent NDP kinase activity in E. coli and L. lactis due to a wide substrate scope . Studying the T. maritima genome an acetate kinase (TmAK) and a pyruvate kinase (TmPK) were identified. To explore whether the substrate specificities correlate with gene annotation, the 13 described enzymes putatively involved in the phosphorylation of nucleosides, NMPs or NDPs (Figure ) were expressed, purified and characterized in a next step.